It's good that you've shot it a fair bit, that way you can be confident that the gun is OK. Because if you start monkeying with it, you're gonna blow the warranty!
Another thing - are you looking to do this yourself, or have someone do it for you? If you intend to do this to more than one rifle, you might want to buy the stuff you need and just do it yourself. Otherwise, it might be worth it to send it out to Charlie (Bob).
In any case, how does it cock? Nice and "buttery smooth", or is it a bit rough? This is pertinent because it'll indicate how deep you may need to go. Wifey's Shadow was a bit of a rough cocker, so I completely tore that one down to debur it and smooth out some stuff. But the refurb 440 I got was so good out of the box that all I intend to so with it is to address the "spring twang" issue.
Twanginess (often the major complaint with a Gamo) has 2 basic solutions. First (and easiest), the spring can be treated with Macarri's "spring tar" - which is basically a very thick and sticky grease. Second is to make a new spring guide (or size the old one) - tighter fitting guides tend to dampen spring vibrations.
