Hey,
I'll be stunned if this is original to me, but I didnt see it in my search.

Ok, broke my "L" bolt off trying to tighten the alt belts. Wasnt in the mood to spend $40 on a new one. So, I went to the hardware store, picked up a threaded eye bolt, put the alt bolt through the eye, threads through the bracket, used a coupling-nut as the tensioner, and viola, a new alt adjuster for $1.25. Much heftier than the original, too.
Enjoy,
Paul

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Paul
2004 E500 4matic; 72,000mi