Have both 177 and 22. The smaller calibre was the quicker to shoot accurately but now they're about equal out to 30+yds I lose the hold over plot after that.
Breech seal, then the spring, then the piston seal. When I had one the spring broke first, then the piston seal went tits up. Breech seal was never a problem, but it's the easiest to check.
Send it back. In the 10 hours it's taken to get through this thread the gun could be boxed and shipped. If no cost to you then no loss and a fixed rifle.;)