[JCtx]

I've written very specific posts about checking and topping off engine oil. You can search, but in summary:
-The hotter the oil, the more accurate the sensor is, so you need to check level with engine at full operating temperature (10 to 15 miles, depending on outside temperature).
- You CANNOT rely on reading car throws, as it's not consistent. Sensor is at REAR of engine main sump (there're 2), so you need to do a manual reset when car is idling at the same LEVEL spot (your garage would be perfect).
- When topping off, add 1/4L at a time until full.

Next time just tell dealer to add 8-1/2L and give you the remainder 1/2L bottle. When you get home, do the reset and add 1/4L until full. I don't want anybody driving my car 15 to 20 miles, but that's just me. How much to top off will depend how long oil was drained. If drained long enough (usually not the case with dealers), you can expect to add up to 9.3L, like in my case, so buy (or get) an extra quart. You'd also need it in case of oil consumption, which is normal on M3s. I also suck the filter housing dry, so I end up pouring 9.5L in my car. Good luck.