Well no obviously if they are fucked, I just fitted new ones to K39.nooo! dont touch the bellow! it'll most likely disintegrate!
Cylinders:- I dug out all the corrosion on a couple, before I left college, and TIG welded them all up. Took out piston, filled with water before welding though.
One has been on for some time and works ok. I fitted my last good one to the other side.
The other welded one I passed to someone else.
I have a third one I cleaned up and repaired with magic metal. Lasted 2 days
I could weld that one up if anyone is desperate.