1968 C20 Master Cylinder leaking

[cjoenny89]

ok last summer I replaced the passenger rear wheel cylinder as it was leaking time stopped me from doing both sides. After I replaced the passenger side it fixed the brake problem but I noticed a leak around the master cylinder cap.
I would always notice the front brake side over full and the rear low and the master leaking over in the front and terrible when I would pop the cap. flash forward I noticed the drivers side leaked out over the winter so this weekend I finally replaced the drivers rear with the part I bought last year. I bleed both sides in the rear but it the pedal was still spongy. I got my son and we went to bleeding again. and that is when I noticed in the front I good amount of brake fluid on the floor in the front. Not it wasn't the front brakes it was leaking out the master cylinder. It keeps having low rear and over flowing front and leaks out the cap. I even scooped some out the front section and tried again. as soon as I started pumping to bleed the rears it filled the front section the rear was low and it was over flowing and leaking forcing fluid to leak past the cap.
Ok we are the original owners of the truck, original master cylinder truck only has 47k miles on it. no buster jus the original stock equipment.
#1 when it leaked out all winter did it drain the master cylinder (rear Section) and does it need bleed?
#2 is the master cylinder bad?
#3 is the proportioning valve bad?
#4 I have no idea I need help lol
I can not even pump it up to bleed the rear any better with out fluid running over and out the cap on the master cylinder.
Thanks