I have a 1998 Yamaha 25HP 4-stroke that ran well when parked a few years ago, but it was ran in salt water and not flushed. It needed an impeller kit when parked, got around to doing it today and the driveshaft is seized. By that I mean that in neutral or in gear, the driveshaft will not turn. I bought it from a commercial fisherman that said it had high hours but had always been maintained, and that appears to be true. Is it worth it to fix the lower unit, or is a motor this old not worth fixing? Thank you.