If there is voltage going to the window motors,replace the motor.When you pull it apart you will never get it sealed again & always have an intermitten problem.These motors were bad enough when they were new.If the switch does not flow good amperage find another one.
Here is some info to help you ,I believe yours will be the first design.You will need to drill out the rivets to get regulator out of door.
FrontEXCEPT 1995-96 CHEVROLETSee Figures 1 and 2
Fig. Fig. 1: Front door power window regulator and motor-96 Chevrolet
Fig. Fig. 2: Front door power window regulator to motor attachments - except 1995-96 Chevrolet
CAUTION The regulator lift arm is under tension from the counterbalance spring and can cause personal injury if the motor is removed without locking the sector gear in position.
The door window regulator motor on these vehicles cannot be serviced separately. Replace the regulator and motor as an assembly.
CAUTION Do not attempt to service the regulator motor separately. The regulator lift arm is under tension from the counterbalance spring and can cause personal injury if the motor is removed from the regulator. RearEXCEPT 1995-96 LUMINASee Figure 3
Fig. Fig. 3: Rear door power window regulator and motor - except 1995-96 Lumina