Brake issue

Probably time for a new master cylinder. They can internally leak, particularly when the o-rings are cold (think space shuttle), and fluid can bypass without building much pressure in the lines. Should be a cheap fix.

i agree, time for a new master cylinder. my recommendation is to get a dual master from a 67 mustang to match your system(disc/drum or drum/drum). it is a bolt in master, but you will have to change the lines to allow for the dual master. i also recommend that you change the flexible lines as well since they are likely 41 years old anddue for replacement, about 15 years ago