Good points. Vintage Corvettes in particular can "pump water" (and air) into the system due to rotor runout, and other disk brake designs may be similarly affected. Drum brake designs are somewhat immune from this because they aren't subjected to direct splash or piston oscillation when the brakes are retracted.

But vintage cars are often not, at least intentionally, driven in the rain and are usually garaged, so they see less water splash and condensing humidity than a typical daily driver.

DOT 5 fluid does not eliminate the brake fluid change requirement, but it means that on a typical well cared for vintage car, you can probably go 5-10 years without ill-affect, especially if it's a domestic that has a "sealed" master cylinder cover. Most European and Japanese designs have a vented fluid reservoirs, which is a moisture migration path.

Duke