A common weak point in the MKI MR2 is the nylon gear on the power window motor. This gear has a tendency to strip, at which point it will no longer raise or lower the window. Toyota only offers this gear as part of the power window motor, which makes replacement a rather pricey proposition.
In the past some people have had metal replacements machined so that they would not have to worry about it stripping. We feel that metal is not the right material for this application, as the gear is no longer the weak link in the power motor system and there is a good chance you can burn out your window motor should the window ever meet resistance on the up or down stroke.
The Twos R Us replacement gear is precision cut from Delrin with a press fit center gear section.