Yep did some trouble shooting and it's Definatly the brake booster. Guess it has a leak internally so I'm going to replace the whole unit and master cylinder from a 1979 wagoneer. For some reason at the parts store they didn't have one under any cj models but did for the wagoneer. It looked the same as the one I have on there. Hopefully it works.?
I was 4x4 in low all night long then it started to leak. 35" tires plus upgraded axels doesn't help I'm sure, but it looks original so maybe it was just its time to retire?