Is this rear main seal leak?

Hi all,

I had purchased 2013 M3 Coupe back in September and had an inspection done at the time. There were absolutely no leaks. Mileage on the time was 34,140. I have since driven it a bit and its now at 35,202 so only about 1,000 miles.

I dropped the car off to a shop to get rod bearings replaced and it is supposed to be a reputable shop. However, as soon as it goes up on lift, they call and say they believe its lilely a rear main seal leak. Apparently, the transmission needs to be removed to reach the line and is almost $2,500. There is no overlap between a rod bearing job and rear main seal.

Upon pushing them a bit further, they said it could be the oil pan gasket and they will let me know tomorrow.

Question to the experts:

Does this stain look like its been there for a bit? I have had no leaks on my driveway.

Pictures attached.

that looks pretty fresh, and is the area you'd see it in. and unfortunately i tend to agree that there's no material overlap between the two. getting the seal out requires dropping the trans, and you don't need to touch the trans when doing rod bearings.

That looks very fresh.

Oil pan gaskets on these things are typically fairly good since it's just a thin piece of metal with nothing to degrade much.

It could be your oil sensor gasket, but it's hard to say. The stiffening plate and air ducting needs to come off to really make a fair assessment I think. If you have DCT, it could be the heat exchanger that's further up.

Once they remove the aluminium undertray and transmission garud which is removed during rod bearing service, they will be able to get a better look, have them call you and send another pic once they are at that point.

I would say it's unlikely to be the rear main seal, but lower mileage cars that were not driven for a long time, can have odd issues pop up with oil seals.

Where is that just-out-of-the-bottle oil coming from? It can't be from the engine, no doubt. That looks more like a splash of brand-new oil coming from the top. You can change the engine oil 10 times in a row, and no clean oil will ever come out. Regardless of where it comes from.

KawBoy wrote

Where is that just-out-of-the-bottle oil coming from? It can't be from the engine, no doubt. That looks more like a splash of brand-new oil coming from the top. You can change the engine oil 10 times in a row, and no clean oil will ever come out. Regardless of where it comes from.

I don't follow, can you elaborate?
If it's sarcasm, just let me know.

kolosy wrote

that looks pretty fresh, and is the area you'd see it in. and unfortunately i tend to agree that there's no material overlap between the two. getting the seal out requires dropping the trans, and you don't need to touch the trans when doing rod bearings.

When you say pretty fresh, what does that mean?

The shop is recommended on forums for rod bearings in the Bay Area so I would not think this was anything other than the actual leak but I am skeptical. However, how bad does luck have to be for this to occur a 1000 miles later?

itrocks4u wrote

I don't follow, can you elaborate?
If it's sarcasm, just let me know.

No, it is sarcasm. That oil is not from your engine. Engine oil, even after a fresh change is going to be dark. The oil pan holds some oil you can't remove just by opening the drains. When you add new oil, it will get darker than the fresh one you just out it. The yellowish stain you have [at least that's what I see in the picture], can't be from the engine.

itrocks4u wrote

When you say pretty fresh, what does that mean?

The shop is recommended on forums for rod bearings in the Bay Area so I would not think this was anything other than the actual leak but I am skeptical. However, how bad does luck have to be for this to occur a 1000 miles later?

It looks almost like new out of the bottle. I can't imagine where that oil is from. Unless you have had a recent oil change and some oil from the oil filler spilled, I really don't know where a clean oil like that is from.

Forgot to mention on my previous post; I am not the sarcastic or sardonic type. My only intention here is to help as I've had help from others. My comments are always meant to be constructive. If I can help you, just let me know.

KawBoy wrote

It looks almost like new out of the bottle. I can't imagine where that oil is from. Unless you have had a recent oil change and some oil from the oil filler spilled, I really don't know where a clean oil like that is from.

Forgot to mention on my previous post; I am not the sarcastic or sardonic type. My only intention here is to help as I've had help from others. My comments are always meant to be constructive. If I can help you, just let me know.

we had the same looking oil coming from the same spot on hcgk01 's car and it was the rear main seal. oil will look like that if it's relatively fresh, it's not like it instantly turns dark the second it hits the engine block. on a low mileage car like this it's not surprising (the oil color, not the leak itself)

itrocks4u wrote

When you say pretty fresh, what does that mean?

The shop is recommended on forums for rod bearings in the Bay Area so I would not think this was anything other than the actual leak but I am skeptical. However, how bad does luck have to be for this to occur a 1000 miles later?

you asked if it looks like it's been there a while, it does not. that said, it doesn't mean the shop did anything wrong or is trying to mislead you. stuff doesn't leak until it does.

Thank you for the replies so far. The shop called this morning and said after completing the rod bearing job they observed a leak so are certain it's the rear main seal. I asked if they can share a few pictures on what it looks like. They messaged then saying that the technician had cleaned it via a degreaser and they will run the engine again for another 45 mins. An hour later, they called saying oil is not leaking anymore and they cannot say if its main seal lwak. I asked them to run it again for longer. In the afternoon, after another run, they said they don't see the leak or its "very mild". They said to take the car and we will do another oil change after 1,000 miles on new bearings so will assess then.

The sent a video (see YouTube link below and attached) and another picture but I cannot tell any leak at all. Plus the yellow stain is completely gone with the degreaser. I don't get it.

What do you think?

In the picture where I circle in red, is that oil leak?

I will not comment on the shop.
Don't let the engine idle for that long; engines don't like to idle. Even Diesel engines.
I would take the car home and enjoy driving it. Keep checking your garage/parking space for leaks. When it is time to change the oil, have the seal checked. The red circle doesn't look like a leak to me, at least not just yet.

KawBoy wrote

I will not comment on the shop.
Don't let the engine idle for that long; engines don't like to idle. Even Diesel engines.
I would take the car home and enjoy driving it. Keep checking your garage/parking space for leaks. When it is time to change the oil, have the seal checked. The red circle doesn't look like a leak to me, at least not just yet.

Good point. Excessive idling just adds to fuel dilution in the oil and isn't good.

But yeah. Agreed. Drive the car and place close attention to the oil level and where you park it for any leaks.

From the rod bearing DIY guide (https://www.m3post.com/forums/showthread.php?t=1333638)

SYT_Shadow wrote

Lots of people finish this job, bolt it up and then find oil leaking onto the floor. This is because when you remove the oil pan, oil starts dripping into the bellhousing and then leaks out later. Make sure you use a towel to soak up any oil that's on its way back there!

Could this be whats happening here? Maybe they didn't catch the oil pooling up in the bell housing. If it doesn't come back this is a reasonable explanation.

Edit: Oops, you can probably disregard this, I misread and didn't realize it was there before the RB job.