2002 Ford Ranger XLT
V6 4.0L 4x4

Hi. I've been having problems with my braking system. At times the pedal will lose almost all of it's pressure and will go most of the way to the floor. It seems like after I've let it sit for a while the pressure will come back, sometimes for a few days other times only for a few hours. When bleeding the brakes I'm having a helluva time getting anything out of the rear wheel cylinders. Now just yesterday I started getting fluid coming out of the cap on the master cylinder. From searching around on the web I've seen many mentions of a RABS valve, but from what I can gather, the XLT doesn't have the RABS, instead it has the 4 wheel ABS. There doesn't seem to be much info out there that I can find. I'm thinking that because fluid is now coming from the top of the master cylinder that the lines are plugged up somewhere and I have a feeling that this valve, if it exists might be the problem. I can't find the location of it though. Does anyone have any idea where the valve might be located? Any other ideas on what could be causing this problem? Thanks!

Oh, also the fluid has a greenish tint to it. Doesn't seem right. I'm wondering if it got contaminated somehow. I'm planning on flushing the entire system this weekend.