This was an ugly feature of the entrance door on our 88 Excella. Nothing would shift the red stain, and I assumed (probably wrongly!) that it was a reaction to ultra-violet light from the sun. I went to a lot of trouble to source the original material, had it cut to shape by a machine company, and replaced the discolored material with new. Although the finished result was good, I now consider that to have been a waste of time, energy and money. I would now spray the material with a Krylon matt paint. This is a $3 dollar (can of spray paint from Wal-Mart) job, taking perhaps a couple of hours. There are previous threads, seen via the "search" facility on the Interior restoration forum, that will describe preparation of the surface. Nick.
Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."