I can't help you with Hasselblad but I have been disappointing by Mamiya RB and RZ. Buying from a reputable used camera reseller, I had to go through 5 bodies and 7 backs to get a leak free and mechanical problem free unit. My first MF was a 645 Super that had focusing problem and died right in the middle of a shoot. It's a used camera with potentially very heavy use by previous owner(s).

I think your only choice is to get it overhauled or at least get it checked out by a qualified person, then make an informed decision on what to do next.