I have people ask me to repair other maker's airguns because they have gone out of business or, as one owner told me, that the maker was too busy to repair guns (of his own make). These circumstances are just a plain "no".
Another circumstance is that there are no parts because the maker was playing it by ear as he went along. The owner has to return the gun so a replacement part could be made; "when he gets around to it". That's why I was asked, because it's been months and months and he hasn't go around to it.
I don't repair or make parts for other people's guns. I have repair parts for my guns on hand. If you had sent one of my guns to a tuner and it has a problem, return it to the tuner to get repaired. I'll repair a tuned gun, but you have to understand that I have to return it to original condition. Any of the modifications of the tuned gun are undone with replacement with the original parts.
A modified gun does not disturb me. I'll fix it. I won't blow the person off by saying "the gun has been hacked".