I received the replacement parts from my (reputable) supplier last night - he assures me they are what the factory uses.

The tensioner is made by Febi (FErdinand BIlstein) and the guide rails are made by SWAG (embossed on the inside). Both also had original MB parts numbers on the wrapping.

We'll see what the originals are when I remove them, which will substitute fact for conjecture.

Experts may wish to jump in here, but am I not correct in saying that MB actually makes relatively few of the parts in their cars? Bilstein shocks, Bosch electronics, bulbs, wiper blades and fuel injectors, various brakes (ATE, Bendix, Girling), water pumps (Lemforder, others), power steering pumps (Siemens, others), alternators, diesel turbochargers (Garrett), glass (Sekurit, PPG, Sigla). Air bags come from the guys who made the defective O rings on the Space Shuttle (at least mine does). I suspect the pistons are sub-contracted and I wonder whether all the rubber parts are too. That leaves them 'making' the design (or do they farm that out like in Formula 1?), the body (the paint is from Sikkens? PPG?), the engine casting and the transmission? Oh! and let's not forget the 'herd of Schwabian cows' that make the leather (quoted from my 1990 560SEL sales literature!).

So, what does "factory MB" mean? I submit that, for most of the replaceable parts which this tech forum addresses, that means something made by any number of independent manufacturers.

BTW, while I still wear my Prince of Darkness T shirt, honoring the great Joe Lucas, I tend to keep quieter about it since I noticed that the brake booster on my wife's 2000 E320 wagon is made by none other than Joe himself......