new proportioning valve leaking

I'm swapping to disc brakes. I installed my new proportioning valve [Edit: I thought it was made by Inline Tube but it wasn't--the picture is from their ad and my valve looks the same but doesn't have the INL marking], connected all the lines, went to bleed the system and found fluid leaking out from the base of the hexagonal piece on top where the front brake line comes in from the master cylinder (see picture). Has anyone else had this problem? I tried tightening the hex part, but it seems pretty tight already.