..in today's "disposable" marketplace, there's no profit in repair parts for equipment that's so durable, repair parts are rarely needed.
Although the simple rebuild kit is PRICED the same as a throw away head.Over $100 for the kit.
The Skipper or the Groco K , would be first choice for replacing a failed complex electric or vacuum setup.
Esp if someone were going cruising.
Moving the lever to flush is less effort than lifting a fork to create the waste.
For folks that have the room almost directly under the head for a tank, the RV units are superior.
The volume of water for each flush is tiny compared to any marine unit , allowing a smaller tank, or longer between dumping.
In our boat LUCY , a rebuilt Skipper , does the job.
Seawater is used to flush , when a cruise is over fresh is used to fill the bowl , so no low tide stench on returning.