Not sure about the grease but I replaced my tensioner and bolt at 292k last year. The original was definitely galled and grooved out. The car has had 3 of the "shocks" that keep the belt from bouncing in its 23 years and in my opinon of watching these shocks that seems like the part to watch. Soon as the shock starts bouncing the tensioner pivot then moves a lot. Not to mention all the noise the shock makes banging.

Kudos for the craftsmanship, I enjoying tinkering as well. I open the hood on my E300 still just to look things over even thought its the most reliable car you can imagine!

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1995 E300 (W124)
1999 ML430 (w163)
2011 GL350 (x164)
2016 Sprinter 144" 4X4 lowtop (906)
2004 E500 (W211) 4matic Wagon (Gold)
2004 E500 (W211) 4matic Wagon Avantgarde (silver)