Hey guys,
thought it's time for a short feedback.
After struggling with it enough I brought the car to a shop, there where some other things to do anyway.
Result in this pulley matter was, that pulley and fan have been replaced, belt is still the same. No squealing of the belt or cracked belts so far. :knockonwood:
Though never change a running system (and now it seems to run), the water pump hast to be replaced as well, maybe because of my over-tensioning of the belt it started to make noises... The mechanic simply has forgotten to replace it.
The car was away for two months, ofc. during summer... so I'd really like to drive it a bit for the rest of the season, a few weeks, 2-300 miles maybe. Hope the pump can handle that, I'm not willing to let her in the garage again until I get parts and have time to replace it...