Brakes on a 91 LeBaron Convertible

Hi, I recently purchased a 1991 Chrysler LeBaron convertible. It's a V6 3.0. We replaced the brakes all the way around, everything but the lines. When we went to bleed the lines, only one side bled so we then replaced the master cylinder. Now, all of the brakes can be bled with the exception of the drivers side rear, fluid drips out slowly but not enough to bleed them. Took it for a test drive to see if we could work any air out of the line and figure out why it won't bleed and only two of the four brakes are working, the front passenger and the rear driver side do not work whatsoever. Someone suggested this might be caused by a vacuum booster but I am trying to get another opinion before I spend $80 on the part. Hope someone can help! Thanks!