I would love it to be a straight forward warranty claim but 2 dealerships and BMW customer services are so far claiming its not a warranty issue.
Perhaps if i lived in South Africa?
Oh and the bike is as genuine as the day it left the showroom.
I don't doubt that the sun, at the right angle, through a standard screen can be focussed enough to generate sufficient heat to melt or distort plastic. The same sun, through a chunk of broken milk bottle, can start a forest fire that destroys hundreds and hundreds of acres. It's rare but it happens. Honda had precisely that problem with out-of the-box FireBlades.
I assume that the bike is still within its two year manufacturer's warranty? If so, it's a BuMW problem. This is better as BUMW can chose to repair or replace anything they like. More often than not they are obliging.
If not (ie, the vehicle is out of the official manufacturer's two year warranty) then things may be a little less clear as:
(a) You will probably looking at some sort of insurance based cover, assuming you have bought extended warranty. This may have BuMW's name on it, but the insurer is independent. The outside influence of heat (which is what sunlight is) may well be excluded by the policy, in the same way that fading of bright work and paint (due to sunlight or the elements) may well be excluded, too.
(b) If you have no extended warranty cover, then BuMW have no obligation to help you at all, unless the problem manifested itself within the warranty period. You are then appealing to nothing more than BuMW's (or a dealer's) goodwill.