A lot of people use this stuff. It worked for me; http://www.renovointernational.com/ or you can buy it here; http://www.partsforsaabs.com/advanc..._description=1&keywords=renovo&checkbutton=Go
The renovo cleaner works as well as Autoglym. Agree with Dan, don't just paint over it.I clean convertible roofs very regularly, and i'd use the Auto Glym Roof Cleaner kit 1st, followed by the Renovo.
Do not use Renovo on its own if you have green algea on the roof, you must clean that off 1st.
The Auto Glym kit is excellent for the money, however a good covering with Renovo afterwards will also be needed.