Same stuff as Malco leather and vinyl cleaner.
Seems its only the white vinyl. My 06 X2 is the same way if the OE MC cover sits on it for more than a few hrs in the sun.
But my buddies 06 X15 with very light grey vinyl does not do this. His sits all summer on a open lift with a MC cover and no discoloration.
It's a problem inherent to the white vinyl.
'06 X2 MCX
"I understand why some people may not want to do this the way I have recommended but I can't understand the death grip some people have on a toilet plunger with a hose fitting." -JimN