Sony had to come replace all three of my guns under a warranty/recall. The service guy said it was $1000 in parts alone for the three guns + the 2.5 hours he was at my house replacing them and re-doing the convergence.
If it needs more than just taking it apart and cleaning everything you’re probably much better off putting your money into a new set.
That being said, these three gun projection sets sure seem to hold up well. Mine is 6+ years old and is on 5pm to 11 or so most nights. I took about an hour this weekend and redid the 64 point convergence and it still looks amazing. I was just looking at my neighbors new plasma and can honestly say mine looks just as good. It can’t upconvert nearly as well as a new set though.