The sunroof on my recently purchased 87 420SEL does not slide or lift, something I knew when I bought the car. I used the tool to open the roof to check cables, etc. but when almost half open it became very hard to turn the wrench. So I decided to close. When I got to within four inches of closure the plastic nut broke and I can go no further. I have the CD for the 126 chassis, but it does not address this situation. Can anyone tell me what to do?