Diagnosing Belt Tensioner M103

[OM618]

Backstory:

1991 300SE

I broke down and found the belt to be very slack and not charging the alternator. I tightened it up but it happened again. Further investigation reveled that the 19mm torque bolt had fallen out of the tensioner (gone for good), causing it to slacken while driving. Through my own stupidity, I continued driving the vehicle while periodically tightening the belt when necessary. This was simply because it was my only transportation and I didn't have time to work on it (even though it was just replacing a simple bolt, ARGH!) during the work week.

Well, driving with a belt that would become slack killed my alternator, which I replaced along with the belt itself. Again through my own stupidity I forgot to also order the torque bolt, which subjected me to having to drive the rest of this week (I work 10-12 hour days, really no time for auto repair during the week) with periodically needing to re-tension the belt.

Well, I went to tension my belt tonight and every few turns of the socket wrench the tensioner would feel like it was tightening a bit, but then audibly click and loose any tension.

I assume this means the internals of the tensioner are shot, but I wanted to run it by you all and ask if it could possibly be the rod or bolt or....something else. Heh, basically hoping someone may be able to suggest that it's probably just the rod, but also to confirm if I'm definitely looking at replacing the tensioner.

Also, what causes these tensioners to break like that?

Thanks,

Vince