The brake release switch is actually a valve for vacuum lines. It is mounted on, or is part of, the neutral safety switch. The switch is on the lower end of the steering column. When the shift lever is moved through reverse the valve opens allowing engine vacuum to pull the release solenoid. If the valve doesnt open, then the valve or the actuating lever is not adjusted correctly. The folks who fixed your trans need to readjust the shift mechanism. Are you also having a little difficulty shifting into reverse or drive, or more likely, lower gears (2,1)?
The manual release is there in case the automatic release fails, a good thing you have this!