ver easy repair, will take some time and you will need some help from a second set of hands, you need to get the motors out of the rear doors. if you have acess to a large rivet gun take the whole assembley out if not you will see 3 small dimple inside the door skin this is where you drill to acess the three bolts that hold the motor to the assembley. once you have the motors out you need un doo a single phillips screw and remove the cover on the motor near the gear. gently pry the gear assenbley out of the motor and drop into some cleaner to remove the nasty grease. there would have been 3 nylon cylinders that are designed to shatter of the window overloads. you need to replace them and the gear if you have stripped yours from the crunching you have heard. do the reverse and put it together and you are all set. it is not as bad as it sounds i have done it at least 8 times on all of my cars
good luck and post any question that you may have
