Hit a snag with my Prop valve/line

That device has two purposes.

1 The proportioning valve is the lower right section

2 The section at top left and what is affected by your broken piece is not a valve, but the brake warning switch

Normally, the piston is centered, and the switch on the left side is OFF. If pressure drops on EITHER the front or rear section of the system, the piston shuttles one way or the other due to this pressure difference. As you can see, there is a recess in the center of the piston, and when it moves either up or down, it actuates that switch.

There actually used to be a tool -----when bleeding the brakes, you could remove the switch, and screw the tool in to the device in place of the switch.

Then, when you bled the brakes, you didn't have to worry about jamming the piston to one end or the other. Sometimes, they could be difficult to reset.

So if you were to 'find' some generic fitting that screwed into the body, you might face a couple different problems-----------

you might have leakage problems, or whatever machine work is on the bottom of the "new" piece may not properly tension the brake warning switch piston, and you'd have trouble there with nuisance lamps warnings. Not sure, but I believe this would also block one end or other of the system not good

THIS STUFF is not something to play with!!!!