To me it looks like a helicoil, the spot nearest the water passage appears to be the end of the coil to me but that's an ugly picture.
If it's a helicoil and it simply unthreaded a tad either grind it down or thread it out and put a new one in.
Your mechanic sucks, if he's making a big deal out of something like this I wouldn't trust him to inflate a beach ball.