As your rig starts to age, you may find that you need to replace your RV toilet.
I have found that my RV toilets have lasted about 9 or 10 years. After this, they may start leaking water around the base.
Since new toilets are relatively cheap, I prefer to replace the unit rather than try to hassle with repairing it. In addition, if you have a white toilet, the plastic may turn yellow over time. This is another reason, why I prefer to replace it with a new unit.
I suggest that you get the same type of toilet that you had in the rig to minimize problems and ensure a good fit.
Check out this video to learn more about how I replaced my toilet in my rig.