I had a RWS and they advised to never keep the spring compressed tto long. An air gun specialist took a spring gun @1,100 or 1,200 fps and kept it cocked for an extended period of time. It reduced the FPS down to 950 fps or a bit lower.
He said pellets were more accurate @ sub sonic velocity- advised people not to try it at home. See if you can try a chrono it - if it's still up to std and accuracy hasn't suffered - all is well