From the pictures you sent and what I have found as far as info on the inching system on this........there is no brake line going to a inching valve....there is a electronic brake sensor(transducer) that is mounted on the bottom of the master cylinder,this sends a signal to the Trans enable valve on the Trans control valve Assy on top of the Trans.
The casting where this valve is mounted has a number 5 cast into it,in your pictures it looks like this valve is leaking some as it looks all wet/grimy around the valve....it is possible that your valve may be sticking is why it is doing what it is doing.....