I have had to replace the driver door regulator twice and the rear passenger door regulator once. It is a common problem on these cars. But it is a relatively easy fix. The parts are readily available and not that expensive.

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1990 190E 2.6
1996 Grand Voyager 3.3
1985 Mustang GT 5.0 5 SPD
1982 Suzuki GS 750T