Trailer abs and brake issue.

Greeting everyone. Another lesson learned that I hope will help others....

Had a issue with the trailer abs coming on in the screen on the dash. Solved the problem , for a while, with a piece of cardboard, because it would blink incessantly. Of course that didn't work for long and I also found that the trailers and the trailer dolly brakes would sometimes be hot enough to stink all the way up to the truck. It got more and more frequent until I got a IR thermometer. I shot the brakes when I got hot ones and some got up to 530 degrees!!
Initially people said it was the trailers and such, but it was happening too frequently. Talked to some people and they figured it was the service line valve since the trailer abs is tied to that valve, not the emergency line. I had the valve and both abs valves replaced, seems there are 3 valves together, but trying to figure out which one is harder than just replacing the whole thing, I figured it was done. Sad thing is though, I was still showing pressure on my brake application gage. This gage, which I thought was redundant, was always 0 until I happen to see it one time and it showed 5 psi. I stabbed the brakes and it dropped to 0. I had been trying to find a pattern to the whole thing since it started. At least now I could see when the brakes were dragging and fix it. That only worked for a while. In fact it was the night I was running with the new valves in that it locked up on me. Luckily I was at the terminal so I could pull over there and called my mech. He came down and we finally figured out (in the rain of course!) that it was the valve under the pedal. I bobtailed it back to my home terminal and parked it for the night. The next day my mech came out and pulled the valve under the pedal out and rust was preventing one of the valves from closing causing air to always be travelling down the line to the brakes. He asked how long since I changed the air dryer filter?? Uh, never. SOOO new filter put on the next day.
I do believe that all the filters have been changed in the truck since I have bought in last thanksgiving.
OIL FILTER *3
FUEL FILTER*3
ANTIFREEZE FILTER
AIR DRYER FILTER
CRANKCASE BREATHER FILTER
FUEL/WATER SEPARATOR *2
If there are any more, please let me know. Don't need to lose 2 days of work for something so simple. Nor buy parts that DON'T need replacing!!

Thanks.