Anything used is a gamble...even new rigs have problems, but they have a warranty.
The facts are:
Mileage wears out parts...and your are talking gas (Class C).
Age wears out everything except metal. Plastic and rubber parts get brittle.
Rubber seals in the engine begin to leak.
Anything that gets a lot of sun exposure gets UV damage.
For me, I can do most repairs, except rebuild a diesel engine
So many repairs come down to the cost of the parts...and most of the time, not a big deal.
However, if I had to pay for all things to get fixed, it would be a different story.
For you, consider your expected mileage, and how long you want to keep the coach. If you will live in one place for 6 mo. the engine mileage may not be as important to you.
If you can, a $35 oil analysis will tell you a lot about engine health...a very worthwhile investment.
Tire age is important, old tires should be replaced even if they have tread left. If your not boondocking, battery health may not be that important.
Best of luck,