Yes, it can leak again. Mike Legere (another forum participant) bought a boxster from a dealer here in Houston and developed a RMS leak about 6 months after ownership. He took it to the dealer where he bought it and was told it had been replaced a year beforehand... so they replaced it for the cost of the part, which was $195 or something like that.
I've heard that the Cayenne's RMS fits the boxster and they're using it with great success now, but you have to specifically ask for it or order that part, and it must be handled very carefully. If the rubber is pinched in any way, it won't work.
Now let me put your mind to ease after I've scared the crap out of you with the comment above, which I just had to put in because it's the truth... if your boxster had the RMS replaced before, it probably won't go out for a long time. Mike's issue was unusual, and the dealer said that too, hence the discount they offered.
Blinkwatt, I really want to encourage you to enjoy your car and not worry about RMS leaks until it happens to you, because it may not happen to you at all! When I first bought my 97 box last year I got very worked up over this very issue because I thought "if I had an RMS failure my engine would blow and then... oh my I don't want to think about that!"
From all I've read, RMS failures start as a drip on your garage floor and you have time to fix it before it gushes out and blows your engine. Just keep an eye on your garage floor and enjoy your wonderful Porsche convertible
