brake question

Having brake troubles with my Torino, soft pedal, goes pretty much to the floor without appreciable stopping power compared to when I first bought the car.  Replaced master cyl, front lines, rear wheel cylinders, bled the brakes several times, but still a soft pedal that's now been there for 4+ years.  The car will stop, just not with a great deal of confidence..  There is an assembly that in the manual is called a distribution valve, but isn't supposed to be on my car (was there when I bought it)..  This is just downstream of the M.C., and has what appears to be what the manual calls a bleeder valve on the front (there is a rubber plug with a pin sticking out of it, the pin moves slightly when you put the brakes on).  The front calipers aren't leaking either.  I don't have access to other intermediates to see what they have, but I need to get this taken care of, any help would be greatly appreciated.

I bled the M.C on the car, and used a rubber mallet and the pedal to work out all of the bubbles, (about 45 min worth) I also used up about 1.5 liters of brake fluid bleeding each corner..  The next two steps I'm taking unless I get a revelation is to take off the dirstribution valve and clean it and verify it still finctrions propery, then take the car to a shop and have the fluid power flushed..  This is the third MC I've had on the car since the problem started (replaced the one I thought was bad 3 years ago, then just replaced the replacement a week ago)  The other thing I want to try is the trick where you use a pipe plug in the M.C. to seal off the front circuit then the back circuit, then both to verify which area is having the problem..

Thanks and please keep the thoughts coming, I'm open to any and all suggestions.

Jim