Think you just need to accept you didnt check it over properly mate and have bought a car with some issues, we've all been there.

Do you have a mechanic you trust? I have seen it so many times, mates going to places that are meant to be specialists or 'sound' and been taken to the cleaners. Sort out what needs doing, get a decent place to price it up and way up if the car is worth sorting.

20 year old RST's are going to have issues, and will constantly and rot hides everywhere, the wiring is getting on now and years of people fettling and messing around doing diy work with little clue can create nightmares. All part of owning one unless you have the bucks to get a properly sorted motor.