Frank - I re-started the DOT 3/4 versus DOT 5 controversy sometime last summer. I would have preferred using DOT 5 also as I've had no trouble with it in my old Corvette for 20 years. But, the consensus of most (but not all) was that some of the seal materials used in the master cylinders and clutch slave cylinder have not held up with DOT 5. So I paid close attention to trying to tightly seal all the brake and clutch line components and went with DOT 5. I think you would be asking for trouble in trying to switch after several years since the old fluid has to be thoroughly flushed out.
I think you are right that the rubber seals may make the paint issue irrelevant.
Keep the posts coming. I can't keep pace with your strive for period correct details but I find them all facinating and adapt a good deal of them.
