I had a water leak behind my shower and found that it was leaking through the soldering of a copper pipe. There's a threaded male connected and the copper pipe was going inside of it and sealed with solder instead of using the thread, so I decided to cut the copper pipe and use a threaded female connector that would work with PEX. There is only about 4 inches of clearance in the wall I'm working in and have been avoiding to cut the wall away for more room because of a piece of wood that would still be blocking the plumbing. I've done my best to cut away the copper and have started to use a Dremel tool to grind away the remaining exposed copper and soldering to try and make it smooth so I can make a seal but there is still some leaking.
I am using ½" PEX with this adapter and a worm clamp to attach it to the threading with an o-ring inside of it. I'm using Rectorseal T plus 2 thread sealant on the threads to help make a seal and I'm tightening it as much as I can. Again, there's very little clearance which makes tightening very difficult.
Here's An angle from the right, an angle from the left, and a video of it starting to leak on the left side when I turn on the shower. I think I need to grind away more of the exposed copper to allow for a flatter surface for the o-ring, but I'm nervous to grind away more of it and am unsure if there is any other solutions to stop the leaking.