Re: Rebuild head, or replace, and with what?
A friend of mine has that exact toilet, and he has had to rebuild his pump every two years. He actually keeps a spare, and just swaps them. I think the Groco toilet is terrible.
You can buy a Jabsco for pretty cheap, rebuild kits are cheap and simple, and they typically last longer than two years.
A Lavac vacu-flush toilet on the other hand, costs a little more, but uses much less flushing water, which nearly doubles the amount of time between pump-outs. The Lavac doesn't require electricity, you can pump manually to achieve the vacuum necessary to flush the toilet.
S/V Old Shoes
1973 Pearson 30 #255