Slow leak repair, shower mixing valve

[willielif]

My stall shower has a Moen mixing valve close-coupled to hot and cold shut off valves, all arranged in a straight horizontal alignment, between a pair of wall studs. There is a slow leak, about 1 drop per minute, at the sweat joint at the discharge end of one shut off valve. The leak has saturated the insulation and started to cause mildew damage. Is there any way to repair the leak without removing the entire assembly from the wall. I have been advised by a plumber that it requires cutting out the existing assembly and replacing it with new components.

[woodchuck]

I would certainly try to re-solder that joint by draining the water out and heating the pipe until it takes some more solder. It might work and would save a lot of work.