Some parts are still available for the older Thetford toilets butt...a replacement makes a lot more sense to me. Used RV toilets (esp 37 years old) give me the heebee geebees!
The newer Thetfords are relatively inexpensive but I know the Bravura models won't fit in the 68.
I like the Sealand brand because they have a vintage look but cost a little more. Many dealers carry them.
If you yanked that old stool out already, you’re half way there. I would replace it but if you are determined to restore it, call any dealer that carries them and see what parts are still available.
Randy...Converters, Inverters, Trimetric, Surge Protectors, Zamp, Smartplug, AGM Batts