Since this is a cassette toilet not a lot of US RVer's are going to have any experience with them, but hopefully someone will come along with some experience.
The 223-S has a rotatable seat. Do you require the seat to be in a non-forward position? That will limit you to what you can replace it with.
As for a replacement, do you want to stick with an electric flush model, or would a manual pump (bellows or injection) work for you?
Salem 29RKSS Pushing a GMC Sierra 2500HD!
Gotta go campin!