While bleeding a friend's brake lines today on his 79 244, I was unable to get any fluid from the left rear caliper....I was using an ez bleed system. All other brakes bled normally. Surely there is a blockage somewhere. Do the rear brake valves ever become clogged or inoperable and produce nothing (not a drop) at the caliper? Or is it more likely a blocked line, connection between the rigid and flex lines---or something else entirely? Any thoughts/experiences you have would be greatly appreciated. Thanks