Vanos adjuster unit issue - cover

[SkinnedKnuckles]

Hi All,

First time poster, have read along over the years, some great posts and advice, awesome stuff.

Hoping someone can help me out!
I have a 2008 E92 M3. Very well looked after, 100,000km. Minor mods, BPM Stage 2 tune.
I have owned this car for 3 years and 50,000km. All good. Replaced alternator a few months ago. Nothing else major to report.

Recently a strange ticking noise appeared, sort of a clacky tick, different to the injector ticking and not deep knocking. Reading all the stories of rod bearing issues had me worried but it doesn't really sound like that type of problem.

Sound is hard to replicate when stationary. Frequency in sync with RPM. Noticeable when driving near a wall or in a tunnel.
I got underneath at idle with my head right at the oil pan, but nothing obvious coming from there. Sounds more like top end, but not 100% sure.

I eventually suspected that perhaps it was the timing chain, and perhaps one of the tensioners was faulty or in need of replacement.

I poked around the engine bay , and noticed through the oil filler cap (looking in there to see if the chain was loose) that there was something not quite right with the vanos unit on the RHS inlet camshaft. The cover/cap for that unit was bent/deformed/bulging at one point.... So, this must be the issue I thought. Off with the covers for a proper look.
Turns out that the cover on that inlet camshaft adjuster unit (which I thought was metal but likely bakelite or similar) is sitting about 5-10 degrees rotated from where it should be, and the alignment tabs on its underside are now causing it to bulge out, because they are not resting in their corresponding slot.

No evidence of anything external acting on this cover to cause this rotation. hard to tell what was underneath, but I assumed that something had acted internally within this adjuster unit to cause the cover to rotate. Could this be the source of my noise? Timing thrown out perhaps..?

So, off came the unit (after buying the special tools for locking the camshafts etc), and I can't work out what has caused this. Took it to the local dealer to talk with a tech - he had never seen this and wasn't sure either. While I was there, I prised the cover off (it cracked in doing so), and we could see that the spring underneath looked fine, bolts in place etc. No apparent reason for the cover to be out of place, and the actual unit appears ok...??

Now, I the confusing part is that I pulled the LHS cam cover off and the LHS inlet camshaft Vanos adjuster unit has exactly the same issue. Same rotation of cover, same bulging!! WTF!
The dealer wants almost $3000 each for these units. I know I can buy them cheaper from the US.
But I am reluctant to just replace them because firstly the one that I pulled the cover off of (RHS) seems to be ok otherwise, and secondly, what if there is some underlying issue that has caused this to happen, and then the new ones do the same thing!! An expensive exercise.

I have tried to attach some photos to show the parts, but I am having issues (perhaps as I just joined?). Will follow-up when I can with more pics to better describe.

I cannot find much info on this "newer" vanos system, to determine how its operation may have caused these covers to rotate (they are very tight e.g. cannot rotate by hand, despite just "clipping" onto the steel lip around the perimeter, which I only discovered after cracking and removing the LHS cover).

I have emailed BPM to see whether their tune may have caused some unusual advance/retard beyond factory limits, as all I can think of is that somehow the spring was "unwound" enough to contact the cover and pop the alignment tabs out of place..?!

I could understand perhaps one unit having some random issue and the cover becoming out of whack, but to happen on both inlet units (LHS and RHS of the engine), exactly the same?! Surely, they were not installed at the factory like this!? Thoughts..?

Any and all comments/advice would be much appreciated.
Thanks in advance!