Over the years my .177 Marauder f&t has gone from 90+ shots down to 60+ using the same amount of air. I noticed it a couple of years ago and suspect hammer bounce since it sounds different from when I first got it. There doesn't seem to be any leaks and the hammer throw and valve are at the original settings; the hammer spring is set lighter than originally. The rifle probably has close to 20000 pellets shot through it. I have replaced the valve and a couple of regulators and most of the seals. Any thing else that I can check?