Many of the aftermarket parts are exactly the same as the parts from the factory, minus the logo. Sometimes there were several OEMs providing parts, all meeting the same specs. These days, manufacturers put these things out for agressive bidding, and may change suppliers from one day to the next. "Just in time" inventory, and all that...
Even genuine MB parts can easily be found outside the MBUSA Dealer supply channel at steep discounts. In fact, the parts supply channel for German cars would appear to be far 'leakier' than that for Japanese or US cars. Not totally sure why this is the case, but I like it.
For this reason, I have found that Toyota parts (for example) can be more expensive to obtain than MB or BMW parts. Toyota must rule their supply channel with an iron fist.
I've learned to dread these words: "Sorry, that is a 'dealer-only' item"
1986 300E 5-Speed 240k mi.