Proportioning valve?
I think you are right, the proportioning valve is closer to the master cylinder.The block you are refering to is pretty much just a T fitting that the brake supply lines fit into ,to supply the rear brake cylinder's. Doesn't it have 3 brake lines in it? Mine sprang a leak on it and it was just a wheel cylinder line. Just clean it off so you can see wich line is leaking and replace the line. Advance auto has lots of diferent sizes
94 Chev Blazer, 6.5TD, 3.42, 4WD,Gear drive,,Remote FSD behind drivers headlight,,Mobil 1 in difs and trans,Rotella 30W, Over a quarter of a million miles !! Member -1.94 club.