Genuine BMW part 67 15 7 006 323: O-ring. The number stamped on the part is 67157006323; BMW's catalog files it under the short number 7006323. You will find it on our Instruments & Electronics shelf, under Other Electric drive unit/system parts.
It fits the E46 coupe (323i, 325i, 328i, 330i and M3, 2000–2006), with the M52, M54, M56 or S54 engines — and the European-market versions.
BMW draws it on the Door Window Lifting Mechanism Rear (51_3687) diagram. BMW's catalog calls for four of these at each place it is fitted. It weighs about 1 g (under 0.1 lb).
We have not had one on the shelf yet. Request it and we will tell you when one comes off a car.