I think you have pretty much got it sussed Gary.
The trim is actually grey and I think black works better (not always but in this case) against the red but even more now I have black wheels and a black top. TBH I would have left it if it wasn't for the staining. I like the idea of the heat gun but if I am going to do anything I might as well go from grey to black and the heat gun will not give me that. Also I am not wanting to spend a lot on this. I should be known as Mr. Quickfix.
I am sure the back to black will wear off sooner or later but it has shown me how much better black is than grey. Pic is a bit blurred.
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I have seen a few FLs with black and am sure.
Sooooo it looks like I need to paint the lot and it looks like I need the Carplan satin that was linked earlier but is now sold out. Also I think gloss would be too overbearingly black. I have seen gloss black on a few FLs' plastic and it is to garish and gawdy for me.