Do you want to replace what you have, or try to add them to something? Someone located the magic silicon oil that can restore them. Don't remember the details, but you should find it here with the search function. If the O-rings wear out, or are forced out of position because the seat is pushed down (it's a controlled leak, and think about hydraulic pressure...it's what stops your car, and the pressure can be extreme). Other than that, the only solution is to replace the seat as the thing is not treated as a repairable item.