If you are able to strip the gun, clean the piston and chaimber with hot soapy water (hotter the better) so there is no more grease or oil. Pay very close attention to the piston seal removing it carefully and again cleaning it with hot soapy water. Once you have done this clean the parts once more with pure alcohol as a final precaution against grease and oil. At this point you can check the cylinder for scoring, if its bad you may wish to have it polished. Assemble the piston into the cylinder using a silicon based lubricant on the piston seal (use very sparingly the lightest of wipes with finger, almost undetectable) The next step is possibly a little more difficult. Take a look at the spring....... wipe with a rag removing all the grease and oil (not to the same standard as the other parts mentioned. Then look at the spring guide. If its plastic and loose fitting, have one made out of silver steel so that it fits with no play! (make sure you accomodate the spring guide in the piston as this runs through the other guide and engages the trigger sear, HW80 that is) into the spring. This is one of the secrets to Dampening twang. There may be after market parts you can source for this. There used to be a kit out there with an ox square sectioned spring and a solid steel guide. Also supplied was a replacement piston seal and lubricants. I doubt if this is available as it would come under the new VCR act. However it is a very simple job for a competant enginear to make one for you. Just dont! fit a bigger spring! This tight tollerance piston guide along with a carefull application of moly grease from a car parts dealer dampens and smooths out the operation of the piston. DO NOT GO MAD WITH THE GREASE as it will make its way into the piston chamber when you cock the gun, and mess up what you have tried to attchieve, and will make you gun exceed 12lb muzzel energy. The next step is to clean you barrel with a copper brush then a nylon brush. Once you have run these brushes through the bore several times use a solvent to remove the lead build up and repeat until there are no marks on a cloth pulled through the bore. I the use Alcohol to finally remove any trace of oil. Job done. Reasemble the gun. And run it in with a tin of pellets, then recheck it with a chrono. Any sign of ignition or a burning smell, you have either not cleaned all the parts adiquately or have used accessive grease on the spring.

Good luck if you get it right you should have a accurate quiet consistant gun that should not need servicing again for thousands of rounds.