Reliability of older Class C’s?

The newer, the better. The late '90s and early 2000s Ford chassis were and still are very reliable. The GM chassis are equally so but not quite as common. Of course, this is predicated on wear items like tires, brakes, belts, hoses, fluids, etc being thoroughly checked and replaced as needed. For RVs this old, however, the condition of the "house" portion is probably more important to consider than mileage on the vehicle. Most motorhomes this old will have leaked at some point, which is not a deal killer as long as the leak was properly fixed and any water damage addressed. But major water damage issues are very common and easily hidden from the untrained eye. Buyer beware.