Well, I bought this nice SSP as a loaner to help create some interest this winter in 10m. Universal stock etc etc. Well, after a few months of non use

I find I have some problems. Specifically, it does not create a full charge. In the last 3 inches of he stroke you can hear a little bit of pressure release. And the pellet POI is now well below where it was when it was working well when I first got it.
So needless to say my act of generosity is now turning into a very expensive tomato stake. Grumble grumble! So, here I am. Asking if anyone might have some working knowledge of this SSP and whether there are any DIY solutions or if I am going to be forced to put some more $$$ into it to make it useful? And if that is the case, who might be the best person to send it to if I live in NH?
Thanks for any input!
Jud