This is a genuine BMW left rear window guide, part number 51 36 8 168 257. The number stamped on the part is 51368168257; BMW's catalog files it under the short number 8168257. You will find it on our Interior Body shelf, under Other Body equipment parts. It supersedes the older number 8130381, so a part carrying that number is the same part.
It fits the E36 convertible (318i, 323i, 325i, 328i and M3, 1994–1999), with the M42, M43, M44, M50, M52 or S50 and other engines — and the European-market versions.
BMW draws it on the Door Window Lifting Mechanism Rear (51_2102) diagram. It weighs about 118 g (0.3 lb).
We have not had one on the shelf yet. Request it and we will tell you when one comes off a car.
