Thetford aqua-magic galaxy starlite toilet

Toilet will not hold water tried high pressure water on seal held for a few days then would not hold again

 

I am a little confused. You said that you tried high pressure water on seal that it held for a few days, and won't anymore. I have a toilet simular to this one in my 5th wheel camper. So I am guessing your talking about one in a camper. High pressure should not be used on a camper, and in fact a water pressure reducer should be used on it. So I am guessing you meant that you tried a high pressure water seal on it. The valve seals on the bottom of the toilet are usually thin, in fact some are felt type material and very thin. If you used a high pressure seal, because it is thicker, trying to fill the gap, the valve may have excessive wear, or something is out of line, and changing the valve or the whole bowl, might have to be done. But consider this, if nothing is out of line, and you used a thicker seal, it will not continue to hold if it does not properly fit in the grove that it sets in. It may have held for a short time because it was resting in the grove, but after working it a few times it will start leaking because of moving it just a centimeter out of line during flushing.
You may have to order the specific seal, by use of Make, and model numers of the toilet, from an RV supply, or the manufactor of the toilet.
My 5th wheel camper sets up for extended periods of time, and I usually pour a little oil (even cheap motor oil) in the bottom of the bowl after dumping and washing. I work the valve to get the oil on the seals, and make sure I have a light puddle of oil left in the bowl, 1/4 inch or less left in the bowl, so that you don't have a dry flush the next time you use it.
I hope this helps, if this is not what you meant by your question, I will be happy to try again, but I will need more explanation of the problem.