'98 Audi A6 1.8t Saloon, both front electric windows have been playing up.. Depress button for window to go down.. drops. Pull up and it shows an inch or so then dissappears back in door, pull it up again and u might get 6 inches.. then it goes back down again.. only way to get it shut is to hold it pull it and be gentle.. WHY?? and how to fix it..???