On one of my first black brant II's i screwed up with my painting and needed to remove the paint.
What i found to work was Brake Clean. A solvent used to clean automotove brake parts. Took everything off, just had to keep spraying and wiping with rags/paper towells.
The trick to this stuff is that it evaporates completely leaving no residue.
Worked ok for me, and the BB II is looking good. I've used this method once or twice since then also and been ok.
It will however eat plastic if you leave it on too long so you have to be careful with that, but i noticed no detrimental effects to either the cardboard tubing or the fins..
Jason