More out of curiosity than anything else, what part of the power window system usually causes the window(s) to stop working?

Is it the central unit (I have a TW) or is it more likely the actual lifting mechanism in the doors that'll give up sooner?

Any preventative maintenance I can do to try to stop it?

(Beside obviously not using the windows) :D

Switch block can develop problems, but can be pulled apart and the contacts cleaned, but wait for it to act up.
There's the cables and motors in the doors as well, but no real preventative stuff you can do.

The driver's side power window on our TJ wagon failed a few weeks ago,stuck in the down position. I figured out how to remove the door trim and remove the power window regulator.As part of the exercise I cleaned the switch contacts as there was a lot of carbon deposit,still didn't get the window to move.I sat the regulator on the ground and sprayed the slider,the wire and every other part that may need lubricating with lithium grease .Still wouldn't budge.After some time the window decided to work again so I put it in the up position until I found a replacement unit from the wreckers. Now I have fitted the other unit and everything is happy again, I decided to have a closer look at the broken regulator. I pulled the motor off the pulley and cracked open the motor assembly to find the plastic gear has worn out a few teeth.I've seen the gears for sale online but they're a bit pricey. Anyone know where to find a cheaper gear? Thanks.