Oil loss on the semmering after changing the belt disc

Hello to the round, I had recently had the large belt disc changed in a contract workshop. After a short time I had noticed a slight oil loss below the new belt disc. Probably the semmering behind the belt disc loosened when pulling off/exchange. Is this a known problem or does the semmering not have to be immediately renewed in the course of changing the belt disc? The workshop informed me that during the exchange d it Semmerings the cooler needs to be expanded again and and and and. I probably have to pay for the further costs. Has anyone had the same problems after the renewal of the belt disc? Are there any experiences? Quite sincere thanks in advance and a sunny weekend!