As stated clean the barrel then test the piston seal, you cock the rifle then hold the barrel down while pressing on the trigger, when the sear releases hold on tight tobthe barrel as slowly let it up. Put your finger from the trigger over the air transfer opening at the end of the compression tube and pump the barrel up and down but not far enough to cock the rifle. You should fell suction and air pressure comming out of that port. If you do then seal is good, if no pressure or suction then seal is bad. A couple drops of chamber lube should also be dropped down that same port to lube the seal. Keep in mind the seal might come apart after a few shots if it has dried out. You might get lucky and be just fine if the rifle still has some of the original lube still inside the seal may still be good. If the rifle does need service, then consider finding a spring compressor, they can be taken apart without one, but if your new at this, there is quite a bit of preload on that spring and the trigger block can easily slip off when it comes free, lots of sharp edges to slice you open!!! That information comes from experience!! If you need to, send me a pm and I can probably walk you thru it.
Have fun!!!
