If you Google leaking RV toilet you will find several helpful Youtube videos on the subject (same goes for many RV issues). If it's simply a toilet issue then repair kits are readily available and not expensive.
We had some cold weather in Oregon this year and if the prior owner didn't winterize the rig then it's possible you had freeze issues .. sometimes those are limited to plastic parts in the toilet .. sometimes a burst pipe or connection.
I live 5 minutes south of downtown Portland .. I have a 91 Class C and if you want to visit I will give you walk through of RV basics .. PM me.