Horrible smell from RV toilet - any recommendations?

We had a dometic model 300 that was know to be defective from the factory and even though it was 5 years old they stood behind there product and sent us a new one. Our whole camper smelled like an out house. I flushed the black tank and put all the chem I had In There and it still stank. "Stuff" was leaking between the outside and the inside of the bowl.