When is it time to replace the rings on a Glow engine?

I have an OS 50sx-h (not hyper). I bought it many years ago and ran it a lot. Sorry I have no actual running hour data. I just replaced the bearings and now it seems to lack compresion, but that is just an unscientific evaluation made by flipping the prop. I am thinking about buying a compression gage and testing all my engines. I have just bought a used OS 1.40rx in a pattern plane. Pattertn planes get run a lot and maybe I need to pay closer attention to rebuilding.