Primered car, needs fixing, and then what.

What kind of air compressor do you have? Will it keep up with your paint gun? If the cfm drops, meaning the compressor is running constantly to keep up, the compressor will get hot putting water into the line. No separator will ever eliminate it.
He should be running a max of 40 psi with that sprayer, just about any compressor should be able to keep up with that.