Help! Our fridge on our boat has been giving us fits. I would replace it but it cannot be removed without major construction. So with that said, I need to figure out how to fix the fridge.

The freezer seems to be working fine however, the fridge is not chilling properly. Earlier this summer, a repairman checked the coils inside the freezer and they were defrosted. So, he welded some sort of thing on the back of the fridge. It has worked fine till now. He told this was a temporary fix. What do we need to do for a more permanent fix? Any help would be appreciated.