brake help

Just take yours apart and clean it. Easy-peasy
You will need some Silicon O-ring lube, to get the valve back in.
The body is all brass, consequently it is practically waterproof, and re-useable until the end of the age..
However since moisture settles out in the lowest part of the system, it carries contaminants along with it like ants on parade. The contaminants are tiny particles of iron oxide(rust). Some of them clump together in tight spaces like the P-valve.
The rubber seals on the valve of the safety sw portion,(there to keep the two systems separate) are almost impervious to anything normally found in the brake system. But I have seen them swell up from prolonged contact with oil. I have heard that they are not available. So if yours won't go back in with the silicon lube, or they are obviously swollen, then you may need a new plan.
Your choices are; 1) another used one, or 2)swap it out for a safety switch and an aftermarket stand-alone P-valve, or 3)Y-couple the fronts together, and separately couple the rears together, and again run the stand-alone, or 4) buy a new one.
As to the proportioning side, I don't recall any seal there. It is just a blow off valve, like a regulator. I threw all those parts away, and have no proportioning at all on my rear brakes Cuz it's really really hard to lock up 295s earlier than the 235s up front.Actually make that impossible; the fronts always lock first and hard while the rears mostly just complain.