For what it's worth, the Old School kit produced around 14fpe of muzzle energy, and it didn't have a lot recoil, haven't had a scope on it but I doubt it will be a scope killer certainly not at 12fpe.
Check the seals (especially the piston seal as that one disintegrate with time), you can check if the breach seal is leaking by using the method above, although I think it's to messy.
I you have a air compressor (10bar or so, not the one to fill airguns and dive bottles), but a piece of rubbery tape on the muzzle (with a small hole in it), and pressurize the barrel, when it's good you hear no air escaping, when you get the compressor pistol of you should hear a "pop", and you know it's good.

Regards, Bart