If you use DOT 5 and don't believe it causes problems, next time you spend a day flushing your brake system, pour the old fluid into a clear container. It will look like layered Jello! It does not mix with water so the moisture settles to the lowest point, stays there and causes corrosion. Flushing may prolong the problems but I don't know anyone who has to flush DOT 3 or 4 from their system annually to avoid problems. It has also been proven to soften most rubber brake parts. We purchased a 48 Lincoln Continental convertible last summer that had DOT 5 installed during restoration, I replaced the entire brake system because of a gooey, stringy mess through out. DOT 5 will also cause a spongey feeling pedal. Our old cars were not made for this fluid and this fluid was not made our old cars, believe it or not.
Gary.