Dot 5 has the advantage of not damaging your paint but it has a couple disadvantages. First and foremost, it does not absorb water like glycol based fluids do. Any moisture will tend to collect in the lowest part of the system and yes.. moisture does get into your braking system.

It also areates easily.. in fact, Harley Davidson says to let a new bottle sit for an hour before pouring it in the system. It compresses slightly more then glycol based fluids too.

It shouldn't harm your seals, but if you do use it, at least change it once in a while.