Lighter fluid in combination w/ the hair dryer works for me. What Rick said regarding WD40!
I did laugh at the WD-40 comment :) It's not really a "special" camera to me, just a camera that's been sitting around. I'm working on the lighter fluid and letting it sit in the sun little by little, I feel a little wiggle now, so it seems to be working.
Have fun! It is absolutely great fun. I have an old Isolette 1 I am practicing on. I decided it wasn't really worth much and so any damage done experimenting was free experience.
My lens came out along with the focusing helical itself, which is not really supposed to happen. I put them both in a small glass bottle, covered the assembly with some Goo-Gone (which for all I know may be as bad as WD-40), and walked away for a month. When I returned the two pieces came apart very easily and all the old, green, goo cleaned out of the threads using only some Dawn dish soap, an old toothbrush, and some hot water. I have not yet re-assembled it, but, aside from a final lens cleaning, everything appears ready to go back together. I have been holding off until I got around to buying some real lens helical lubricant, but have just about decided to just go with a small dab of white grease and some q-tips.
My next step is to construct a homemade bellows as the old one reveals more points of light than the sky at night. :) I have no idea whether it will work at all when I finish but I am having great fun with it anyway.
If the holes in the bellows aren't too awfully big, you can paint them with black fabric paint to repair.
Black automotive type RTV gasket silicone rubbed into the corners that are really bad works works well, too. Bellows end up- a bit stiff but still close.