I have the same exact problem. I have called several RV dealers and have even down loaded the diagram with parts from Thetford. Here is what I found out. Thetford will not sell you a pedistal for your toilet. You cannot replace the part, because it is molded into the toilet. You have to buy a new toilet. I heard that from Thetford customer service a couple of days ago.
At the moment money is tight and I cannot justify a new toilet. Thetoford is running a 35 dollar rebate on new toilets until August 1st. I could buy with the rebate a new Style II toilet for $188.00. That is the best deal I found. I can get it cheaper on the net but shipping would change all that.
This is what I decided to do. I went to a Marine boat store and bought Tex-mex epoxy repair kit. I have used it before and it works great. I coated the whole water inlet on the outside (except the threads) and I coated the whole inside except the inlet hole that is all the way back. I will hook it up in the next few days and see if it works. I think it just might.
Your toilet is held together by two 1/2 inch nuts on each side. That is it. Pull it out and either try what I did or buy a new toilet. You will need a new gasket the toilet sits on.
Brian & Adrienne