I used the service kit for my Jabsco head - worked like a charm. Actually I only needed one gasket, the one that is in the top of the
pump (and controls the flow) and the piston and piston arm. Everything else was in a good shape, just had to be cleaned. Some bleach and mr.Clean and some rubbing and the toilet looks like new (really, it does). I recall paying something like $40 for the rebuild kit, though. In fact, you might be able to just get the one gasket if yours is in the same shape as mine.
There is a parts guide for Jabsco toilets that lists every single one, you can use it to find what you need (I got mine with the kit, though
)