[rohrmann]

Is your Sealand the same as the Dometic? If it is the same as the 200 and 300 series toilets, it appears to be pretty easy to replace the water valve assembly, which is probably worn or sticking. It's either repair or just replace the toilet, not good to risk the expensive damage from a major flood inside. We just replaced our Thetford with a Dometic 310, and was around $200 and only took about 30 minutes to replace.