I have stripped one of these. They're not too hard once you understand the mindset of FB. Most people don't realise the the muzzle is a "nut" that needs to be unscrewed. Once that's done I think the rest follows fairly well.

As for the seal though, you can't get these anymore. A friend tried to make some but the material is too hard really. It needs a bit of flex to make a good seal. Ideally one would try again and make a groove around the perimeter to fit an o-ring. However you also need to seal around the barrel too.

If I was to try to make another seal, I would attempt to make one from thick leather. It will swell a little with oil and seal the pistol better although the friction could reduce the power a little.

Other than the piston seal, the other very brittle part is the little plastic pellet probe. If do not follow the cocking procedure, it's going to snap. You might be able to make a replacement using a 3D printer.

A few people have asked how to service the Champion.... it's about time I wrote a guide!

All the best,
Jimmie