OE are what you get from the dealer, OEM are the same parts sourced from anywhere else. Often the only differences are the absence of the tiny MB logo and a significant amount of money.

Anything else might not last as long or perform as well. I've not had any trouble out of OE or OEM; just try not to use any of the cheaper parts that are out there. Dealer parts are the safest bet but will cost you.

In ATL I'm sure local sources for OE or OEM are too numerous to count.

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'02 BMW 325i
'85 300D 450k
'93 190E 2.6 170k(killed by tree)
'08 Ducati Hypermotard 1100S 6k
'06 Ducati S2R800 14k(sold)