Fastlane Woes: Engine Range vs. Item number

[AtlBenz]

so was there some kind of change to the way Fastlane/Worldpac does their parts? it seems that lately when looking for parts I now have to select from an "engine range" that uses numbers that I know nothing about. As far as I know my cars engine is an M104, Fastlane's numbers:

-12-072236
12-102821-
12-072237-12-108820

dont mean much to me. can you help?

I'm in need of the serpentine belt for my 1995 E320 wagon, but now there are 3 different belts, with 3 different lengths, 3 different part numbers and of course 3 different prices. How can I possibly know which is the correct one for my vehicle?