Braking Issue on Fleetwood Flair

I haven’t looked at the rotors and brake pads yet, at least not with the wheels off. Figured that’s probably where I should start. It kind of seems like a warped rotor but it seemed odd to me that it only acts up when the brakes get hot and not when they are applied. I don’t know about the brake fluid. The RV is new to me so I’m sure it could stand a good flushing. I will also look into the master cylinder. Thanks for the replies!