I can just see Judge Judy (or equivalent) saying "What does this mean? Maybe it makes sense in German?"

I think what the service manager is trying to say is that if the dealer breaks something while removing it, or sees something else wrong while repairing it, then the customer is liable.

Adjusting the valves and breaks the linkage? You pay.
Changing the oil lines and strips the cooler fitting? You pay.

The dealer is basically saying that they don't want to work on old cars because it's harder and they don't want to exercise due diligence - or that they can't pass the cost of "breakage" onto the Corporation under warranty claims.