IH Workstar yellow button valve hiss

Working on my IH workstar and during harvest it developed a squeel hiss when the button is pushed in but goes away when pulled to engage brake, I've done some other reading on here and tried different things

I've pulled the dash apart and checked the valve itself i don't feel any air leaking and tried soapy water and don't see anything, is it possible for the valve to be leaking internally?

I've pushed the button in and crawled under the truck i don't hear or feel any air leaking from the brake pots

not really sure what else to check, my gauge shows I'm slowly losing air when the button is pushed in but i cannot figure out where

 

i gather that from everything i've read but how do i determine which one it is? there is no air leaking or nothing, everything is working fine

 

i investigated the issue this after noon with vice grips and soapy water and didnt find nothing even when i pinched line off the sound in the cab never quit, so i donno what to do from here everything still works fine, might see if i can book it in with local mechanic to have another look/opinion on it