Any good heavy oil on the spring would be ok. To lube the piston, make sure it is a silicon base oil( high flashpoint oil). Put a few drops in the vent hole(where it aligns with barrel when barrel is closed) hold muzzle up and work barrel back and fourth a few times to spread oil, do not go so far as to cock. It should be good to go then. The only thing is considering the age is that you might need a new piston seal and possibly a barrel breech seal( usually an o ring_
Sounds like a recipe for the gun to deisel. You're suppose to use moly on the spring, NOT Silicon oil. You're going to burn whatevers left of the piston seal
using that stuff, and make it sound like a .22LR going off. You're better off using the Pellgun oil instead.
Know about dieseling, that's why I said silicon on the piston. It does not matter what is on the spring, that is not where dieseling occurs. Dieseling occurs inside the cylinder where air is being compressed.
At one time there was a "diesel" rifle made, cannot remember who made it, but it had a small injector that injected a very tiny bit of ether into the cylinder. I read that it gave very high velocities and the pressure created would actually recock the mainspring. Piston seal life was poor.
When that gun was made they were not using moly in lubes like now. A good heavy oil or very light grease on the spring is ok. I have a later model that looks much like that as well as a Fienwerkbau 124 and 300, and none of the factory literature that came with the guns specified moly on a spring.
New seals are always a good idea.
