I'd be looking for another seadoo...If you leave any water in the engine for any amount of time corrosion starts quickly. If you have corrosion internally, chances are the crank, bearings pistons and rings are in need of replacement. A machine that old wouldn't be worth the rebuild money it would take to repair it.
The best advise to give you is, if it is an old seadoo and you can't test drive it, keep looking for another project. There are lots of good used seadoo's out there that won't drain you wallet.
Karl