I would agree with John... David can probably fix about anything. I don't remember any difficult disassembly assembly issues and orings are pretty available sizes.
The value is going to depend somewhat on what vintage and model it is. I had an FT Dragon in the late 90s and had it apart MANY times, trying to get the trigger better and power up a little. Only made 10 ft lb. Years later I was approached to fix a Sporter. It was WAY better made in the valve and trigger area. I would guess it was an earlier manufacture date. Went cheaper as production went on, is my guess. Fast forward to last year... I was given a Sporter that was brought over from England and went through it completely. It was made as well as the other Sporter but had sleeve bearings on all pivot and sliding points. I'm fairly certain that my FT did not have those and can't remember if the other Sporter did.
The point of all that is there are differences in quality through the production range. The one I still have is a BEEFY sucker .... very well made but not powerful and not especially fun to plink with. Still... it IS interesting to shoot and nice to look at .
Bob