1996 S420 Driverside Window Problem
 

My driverside window rolls down half way and then stops as if it is stuck in mud. It rolls back up fine, but will not roll down all the way. I removed the door panel and cannot seem to find anything blocking it from rolling down, the motor is working good. Does anyone have a clue of what to do or any suggestions before I take it to the shop and they charge me an arm for something that may be simple to fix in my garage.