I have a 1974 115 chassis 240D. I've been having issues with the alternator belt losing tension and squealing. My problem seems to be the the infernal way the tensioning works, mostly with the rack that the star headed bolt moves along. The rack seems to move up when I try to use the star bolt to tighten the belt, regardless of how tight the rack bolt itself is. I tried to skip the whole silly star bolt thing by simply levering the alternator with a judiciously placed prybar and then tightening the pivot bolt and star bolt. It seems to hold for one or two trips to the grocery store before the dreaded squeals start again.
I'm using the conti brand belts and have replaced the star bolt and nut.
Somewhat at the end of my rope...my next step is to try and rig up something scary looking with safety-wire and a block of wood to keep the alternator from getting loose...