I.J. can give you the lowdown on stripping them - essential to use spring compressor and also you have to remove the scope ramp to strip the internals.
Mine had that little spring missing, you can make one from a decent quality safety pin once you see what shape it is supposed to be.
They will do 12 ft/lbs easily. Maccari does springs for them, but they need preload on them.
Excellent rifles, a tad crude compared to the Weihrauchs and Feinwerkbaus of the time, but as tough and usable as a T34 tank.