Yes, I know it is 'so cool' to wear your 40+ years Sub while surfing but by doing so you are just asking for trouble. Most vintage watches are NO LONGER water proof so don't just assume that because it's Rolex it's OK to wear it in water.
This particular 5513 came in yesterday in rather miserable condition. In just 48 hours after the water got in, it started to rust! Luckily for the owner it was still not too late - most of corrosion was contained in main spring barrel area. Lucky this time - a close shave indeed!