i think im going to try tomorrow to take the door panels off and lube the window regulators to see if that fixes the problem. it makes sense because they probably havent been lubed since factory. what would be the best type of lubricant/grease to use?

Well, it is possible. You can go the junkyard and find a 240 with manual windows (which are harder to find than 240s with power windows) and take the regulator mechanisms from all four doors, and I believe the armrests; or you can go get two regulators from a 240 with power windows.

FWIW, I have never seen a 240 with failed window motors. I know it happens, but in the six 240s I have worked on, a non-functional power window was due every time to some other problem. Dirty switches were often the culprit. Once, the mechaism was jammed against the bump stop at the bottom of the regulator and it only took loosening the screw to free it up.

Usually, a bit of grease and some clean switches will bring a power window back to life. Youll be tearing the doors apart either way. The real key here, the thing that will probably make up your mind, is that you'll have a much harder time finding manual window regulators than fixing/replacing the power windows.

I've done the reverse - manual to power - so I don't see why you can't switch from power to manual. You'll need the manual regulators and different arm rests and the cranks of course. It's actually not that big of a job to swap the regulators - a Bentley manual will help. Why don't you look for replacement motors? The hardest part of the job will probably be fishing all the wiring out from under the dash through the door jamb. I hate that part actually. It's also possible that your regulators are binding and just need some lubrication. I bet they'll work a lot better just with a simple servicing. Lots of threads here on that I believe. Good luck!