Eagle
I had simular situation with my 88. After changing out the rear cylinder and bleeding the system the brake light would not go off. It stayed on for over a year. Until one day someone pulled out in front of me and hit their brakes. At the time I had not upgraded my master cylinder and booster yet. I stood on that brake pedal like I never did before, including driving an old beat up 51 chevy pickup and have deer jump out in front of me. Anyway, after that the light went out. I am not sure what made it go out, if something reset itself or an air bubble was forced out or what, but it worked. For what is worth, try stepping hard on the brake and I mean hard - test those seat bolts. What can you lose.
PS Don't do it in traffic like I did, especially if your brakes will lock the tires. I would try it at a stand still.