Hello. I just received a new - old Eversharp/Wahl Doric FPN (1936 version with a simple nib). It has a Vac system and they call it "a one shot". There is the problem. The knob on the back of the pen will not budge. I have soaked it in Speedball pen cleaner and the paranoid side of me thinks the fountain pen had been filled with Super Glue. I try to be rational but you know this is my first plunger type fountain pen I own in such an aged condition. I know Medea has an Airbrush Cleaner and that literally will remove tar off streets. Having read on this pen type it seems the plastic is slightly improved but can end up crystalizig due to age since the resin is just made fragile. I am not sure what to do with it and i do not want chemicals to react with that plastic body. Can someone please throw in some recommendations, tips and insights? Thank you.