Not a quick and easy answer - and my knowledge comes from 67-and-earlier B-bodies, but I have a couple comments.

1.) You say the passenger side window slides up and down. That condition sounds like a gear is stripped, not a failed motor. My gear boxes have worm gears which would not allow the window to just slide if the motor failed. I trust you know enough to be sure the motor has failed, because you say the motor makes noise, but I just want you to double check that.
2.) The driver's side problem sounds more like a lubrication problem.

I don't know the best approach to getting the regulator(s) and motors out, but

- On my earlier cars it was not hard to get the motors out. They had two threaded rods and nuts holding them to a bracket with a rubber damper connecting the motor shafts to the regulator input.
- Getting the regulators, gear box and "arms" out was a whole nuther matter and I'm not surprised you wish to avoid messing with them (it's no joke when I say it was the biggest @#%$ PITA of my entire 6-year restoration when I had to remove, dismantle and refurbish all four of mine. And one of them is now skipping its gears, so I've got to get back in there. Oh my head).

Do you have an exploded view of the setup?
Cheers,
- Art