Well, I don't see how you could have a '74 T140E? As Meriden didn't start making the E model until early 1978, in fact there were no rear disc brake (T140V/TR7) models at all before 1975 when Meriden introduced the left foot gear change.
However, it is a possibility that the rubber hose has become collapsed internally. Another very common reason for this problem is usually because someone has screwed the master cylinder assembly too far into the alloy housing, which results in the piston not uncovering the vent port when the brake is released, so the residual pressure within the system can't vent to the reservoir.
