That's interesting. Other people I know have said the same as you but I've had two F91s fail and let water in with light swimming. I bought a W59 which is almost exactly the same (I'm not entirely sure what the difference is) and not had any problems since.

Spent six months surfing, swimming, and sweating through the tropics with an F91W strapped to my wrist. I bought it because it was cheap and I was poor, but I fell in love with it instantly. Lightweight, durable, and accurate as hell, it was the perfect companion.

It's a shame the strap's shitty, though. I noticed a nick along the inside edge one day and thought nothing of it. Got off the bus in San Jose and it was already torn halfway through. By the time I found a place to stay for the night, it was gone. I damn near cried.

I don't have that kind of attachment to watches orders of magnitude more expensive.