Speaking of parts, is there an online resource for MBZ part numbers?

For example, if someone is selling a part on ebay and gives a part number like "124 etc. etc. ", where, besides a dealer, can I confirm that the part is correct for my car?

I have a MBZ parts picture book but there is a different system. Same thing with your typical internet seller, their number id system is different also.

glenmore
1991 300CE