This is a Sealand Dometic Vacuflush toilet that came out of my '93 Casita RV. I planned on using it so I put in a new water valve, spring assembly and ball and shaft kit and it works perfect. It does not leak.
Unfortunately my holding tank is cracked and I will be replacing everything with a self-contained cassette.
These toilets are very expensive and they were used in several brands of RV's. Send me an email with your name and phone number is you are interested and I will call you to answer any questions you may have.