Another issue from professional mantaince stand point is that the rebuild/ replacement is suposed to last another twenty years. Parts that are avalible now may not be in ten years. Having worked on a 125' shcooner that used older technology so that it would match it's sister ship, I can say that you'd be better off replacing it. extra parts may look avalible, but when they show up will have to be modified or will have a shorter life then intended.
An example would be that we had to replace most of the silenoids on the main engine and one of the generators just about every other year. This was because our's where originally 32 volt and the replacements we could get were 24 volt. They worked but would fry out petty quick. All are electrical componants had to be sent out for rebuild. It was rare to find a new or already remanufactored sitting on a shelf. Any time something broke we'd have to either jury rig a temporary sulution or put the boat out of service untill we had the parts rebuilt or refabricated. Even simple items like the pump braket or the transmission linkage, would have to be fabricated or retro fit.
Thats what you get into. It may be that you can still get impellers but there half again as much, only made by one company, and made using cheap rubber. Not like you can go somewhere else to get them. Same goes for gaskets, random brakets, control linkages, electronics, and just about all the stuff that should be no biggy, but becomes a major hassel.
The other thing to consider is doing all the other refitting you have planned including deciding what new motor you'll use when you repower, then leaving the existing engine in place till something big goes.
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