I too experienced the same, sticking brake pedal on my recently purchased 1997 Boxster. After a couple of Google searchs found that there is an update Brake booster and attaching parts from Porsche for lots of $$$. Went on E Bay, found a complete, (including the new style bellows to prevent water intrusion) for $90.00. As John said, it takes about 3 + hours to replace the Brake Booster (I'm sure I could do it in less time the second time around) but now the brakes works well, no sticking. I drained over a quart of water out of the old booster, and with all the rust and corrosion inside wouldn't have given it a second thought to reuseing the old one. John just have one thought, you might want to consider adding some kind of deflector if you are still using the old seal(bellows) or you might have a repeat problem with water again.
Bill
