98 buick rear right window works perfect when it works , but some times seems to have no power to switch and wont go up an down

The power windows on your vehicle are controlled by an electronic control module , as are the power mirrors !
Power Window System Components
The power window system consists of the following components:
• Driver door module (DDM)
• Passenger door module (PDM)
• Body control module (BCM)
• LR power window switch
• RR power window switch
• Window up and window down relays in each of the rear passenger window switches
• Window lockout switch
• Reversible power window motors in each of the doors (circuit breaker protected)
• LT DOOR CB 25A (System power for left rear window)
• RT DOOR CB 25A (System power for right rear window)

Your best bet , take your vehicle to a qualified repair shop.

Check fuse, try switch from other window as they do the same thing. You may need to remove the trim & power the window up manually to check motor works.

I'd check the fuse box for any sign of corrosion and re-seat any fuses having to do with window operation. The switch likely used is a 'double throw, double pole' type with a center rest. This type allows switching the polarity of voltage supplied to the motor to produce both directions and without the car's wiring diagram, it's difficult to tell you which terminals need to be shorted to move the window in the desired direction.There is probably a connector inside the door that completes the path to the car's electrical system and if this has gotten wet, it may be corroded and become intermittent.
For this problem and as a guide for other problems to come, I recommend investing in a Haynes service manual which will contain all the electrical diagrams you need to find this problem and very complete service info on the engine and drive train as well.It would be the best $25 you can spend and may save you thousands in the future:
'98 Regal manual
You can buy them on line or in most auto parts stores.

Yes, replace it, not making contact all the time, bad contacts in the switch.

Probably the master window switch.

All window motors work through the main four button switch, replace it with a donar .

check you master power window switch,it's probably time to replace it.the contacts on the inside of the switch are wearing out.

most of the time it is wires in the drivers door that break in the loom

i have had this issue before all i had to do is do a new ground, jumped the safety window lock, as well as expanding the metal clips in the wire con.