Thetford toilet and the water leaks down pretty quickly. I am thinking it’s the blade seal and I guess that means removing the toilet to do the job. If thats the case, I am tempted to pay someon...
My seal is fine, but I spray Silicone on it occasionally to keep the rubber soft. I shut the water off, clear the toilet of standing water, spray it and let it set for a bit. Not sure if it works on the toilet, but by slides seem good when I use it there.