I've had the same problems with the paint breakdown on a 1992 Marquis roof. It is cleaned up a lot with a good scrubbing with any kind of cleaner, (I used Soft Scrub with Simple Green) and then an application of Mop and Glow. And currently all the white streaks have stopped.
I assume any good cleaning and a good wax is ok. But a better choice is a total repainting. There are a lot of choices, anywhere from paints to elastomeric coatings. I had posed this question on the FMCA forum sometime back, and several responses were helpful.
But the best product is a paint on elastomeric coating with ceramic insulating spheres in it. It is a white coating that has a high insulating factor due to the additition of hollow ceramic balls. About the consistancy of flour. I did find a product that was made for this, called Bus Kote .
http://www.hytechsales.com/prod2150.html, the company also makes a clear coat that can be applied on top.
While this can be more costly, with an undercoat, then the Bus Kote, then the clearcoat, it is supposed to peform well and also increase the insulation effect by as much as 30 to 40 percent. And it can be rolled, brushed, or sprayed. I hope to try the process in the future. But untill then, the Mop and Glow works well.
Regards,
Eddie LeBlanc & Carole Miller
1992 Marquis Regent
Beaumont, Texas