I've been running DOT3 in my '46 since '86. Sleeved the master cylinder in '97, and just rebuilt it in '08 because of a leak. MC bore was fine, the rubber parts just got old and needed replacement. I bleed the system about every 2 years until I've cycled out all the old fluid. DOT3 is hygroscopic (absorbs water) so it will become contaminated over time and, if left alone, can cause rust problems inside your brake lines where you can't see them.
David Bush
