I don't know how many manufacturers there are for RV/marine toilets. Couldn't be that many. Go to Thetford http://www.thetford.com/HOME/PRODUCTS/PermanentToilets/tabid/76/Default.aspx
and see if you can match descriptions. Hard to say how many changes have taken place in the last decade.
My Thetford toilet had a stick on bar code with Mod. # and description. It was located on the underside of the bowl..door side. Thetford uses the "sun with rays" to replace the "o" in Thetford........could have been a change with time.
Good luck.