Recently bought a used keg from a friend of mine for $15. It's in really good condition except that the lid leaks from the pressure relief valve. I took it to my LHBS to get a new relief valve. They put a new valve in, but it still leaked. So, they then took my existing valve and put it into a different lid, and it held pressure.
I'm at a loss. Looking at the lid, without the pressure relief valve in it, there doesn't seem to be any visible defects. I ran water through it to rinse it out, but I was wondering if it was possible that there might be some sort of build-up in there that would cause the valve to not seal properly.
Suggestions? . .. besided finding a new lid.

