Now I have started looking at US suppliers I have the opposite problem - too much choice! There are so many after market brands available in the US.
For example, looking at Pelican Parts for the drive belt tensioner for an ML430, suppliers include, Uro Parts, Litens, Febi Bilstein, Ina, Trucktec, OE Supplier, and of course Mercedes.
Which one to go for?
As an aside, I spoke to Silver Star Spares in Sydney, Australia this week. They quoted me $140 +GST +Freight for the Trucktec tensioner pulley (just the pulley), yet I can buy the whole Trucktec tensioner from the Pelican Parts for US$80.50
Perhaps some research into where certain parts brands are on a scale from cheap junk to middle of the road and road OEM - suppliers and Mercedes parts.
The last two are quality wise about the same, like Lemforder and Mercedes.
If Kim was kind enough to get in touch with you, he has all the experience to point you in the right direction.
In our opinion, brands like Hamburg Tech or URO are close to the bottom. Febi a little bit up with Meyle close to middle of the road.
(German spelled) Autohausaz is near Phoenix, Arizona, and also offers original MB parts. I like them for using the original MB parts numbers, you can use in your browser for a search for best deal on the OEM part.
MBoem parts is really Mercedes Benz of Naperville (near Chicago) I am told.
FCP Euro is not a vendor here anymore but has good prices on same parts, but is on the US East Coast.
Best of luck