there seems to be a port that isn't used by any lines and it just has a rubber plug in it.
It just started leaking recently though.
Does anyone know what that port is for?
Its on the front of the pp valve in the middle of the other four lines.

 

i dunno, but i'd just replace it. it could probably be rebuilt, but they're easy to find from junkyards and stuff.

 

the only reason I don't want to replace it is the fittings on some of the lines are chewed up and they won't be easy to remove.

I was thinking of just pulling the rubber plug out and tapping the hole and threading in a plug.
But I'd like to know what the plug is for in the first place.