I just replaced the 90° cutoff valve because the old washer perished and the valve was shut off very hard. The cutoff was threaded onto a copper adapter which is sweated onto 1/2" rigid copper pipe. I put the new valve on with ~4 wraps of teflon tape, and it had a slight leak. So I removed the new cutoff, gave it 9 wraps of tape, tightened the valve back on, but there is still a slight leak at the threaded joint, maybe a drop every 20 minutes.
I would just replace the sweated fitting, but as the picture shows it's very tight to the wall -- I think I'd have to make a fairly large hole around the area and maybe still run some fire risk.
I'm looking for a creative solution, possibly with continuing to use the stripped fitting.... Would it be possible to bed the threads in epoxy and reconnect the cutoff? Would that use liquid or gel consistency, or a putty type? Is there a way to solder a tube into the adapter or over it? Or do I have to lump it and tear into the wall?
edit, added: wondering if I could sweat threads to threads if I put a FIPS copper adapter or brass coupling onto the male adapter sticking out of the wall. Would that work, in a pressure holding sort of way? The adapter threads seem to be the part that's leaking, and soldering will not depend just on the threads.