If you can not find the master cylinder, you really need someone to find it for you, and show you what they look like. It is under the hood, not under the RV.
The radiator cap is on the top left side of the radiator. It might be difficult to find the top of the radiator, many manufactures have rubber around the top of the radiator, so that all the air goes through the radiator and not around any of it.
My air filter is in front of the radiator, nowhere under the doghouse. I don't know if you have a GM or Ford chassis, I have a 97 Ford. It is important that the air intake is cold as possible, and mine is in front of the radiator for that reason.
I would recommend changing out all the brake fluid, rear axle oil, and transmission fluid flush. Lube all the steering, u-joint and other zerk fittings. The power steering fluid probably has never been changed. This will bring you up to date.
Fred.
