First, I would not be keen on "grease" since it can be a real magnet for dirt, debris, making a bigger mess. There should be an adjustment on the ends of the door at the bottom, for height adjustment. Just turn the screw,slightly, say 1 turn, and see if it helps or worsens the problem. Try the other way if need, but you can always go to where you started again to not worsen the issue. Check for anything binding in the track maybe a dry roller, which you could free up with a shot of say WD-40. Just try and see what's making it bind up, dirt, broken piece of weather stripping...whatever.