Ok, so I got it today. Seems the main problem was it just needed a bit of TLC;
Replaced the hammer o-ring and give it some lube and it seems to be working "ok" - however, the recoil pad is absolutely battered.
It's currently getting about 20 shots from a 12g, and not much over. Could it be the pad that's causing this?
Apart from the spraypaint all over the internals (I mean, really
), I can't see anything else that could be causing the issue.
I'm going to give him a little lecture on taking care of his marker when he gets it back...