Leaky Dash Tractor valve?

I noticed recently that when applying air to remove my tractor brakes (Yellow knob) that sometimes air is heard hissing...long after the brakes are released....it keeps hissing...so if you stop, Pull the valve out and re-push it in, sometimes once it applies air to the brakes, then it stops hissing and sometimes you need to do this 2 times.

So far, it hasnt caused any issues but what's going on here?
Time for a new valve set?

I do not have the foot brake applied when I am pressing in the yellow knob either...

 

<- Yellow face for yellow valve


Yea, that is a serious concern of mine. Either not being able to release the brakes or SNAP/POP and I find out what the steering wheel tastes like at 50mph...

I wonder how hard of a job it is to replace this valve. Doesnt look too all that bad, but thats what I thought about the last few things I have done.

 

I would guess this is similar. AS long as I can do this myself, then thats cool. I have given KW way too much $ lately in labor...

 

Its a combo unit though, right?

We have NO truckpro places here. I have one in IL I have called in the past, but here I have KW or Truckcountry...unless I mail order it.