To answer both questions, yes deliberately vague, but nothing sinister in that for the purposes of discussion, fault was an air leak, and some looseness in the main body (possibly connected to a missing screw or just screws needing tightened) The part is apparently hard to source - not impossible, I don’t tech, at all, so not sure how accurate that is.
in my opinion looking at the disassembly diagram I suspect the gun would not function at all with this part broken. Again….not a tech, so can’t be sure.
my issue I suppose is that I specifically said I would refund if no work was done, I know how tricky these can be from reading about them. And the buyer claims to have detected the potential fault, then instead of asking me first proceeds to dismantle and finds multiple faults. (All minor, missing screw, possible missing small spring, broken £7 part)
if he had contacted me to describe the fault - probably to avoid grief I would have said send it back, and stripped it for parts, it’s worth a lot more stripped than the price I sold it complete
there are some good accessories with it .