So my HL brake light was jaded due to UV exposure as many are. I replaced it with an aftermarket smoked version. Trouble is that the LED’s are so crap that it might as well not be there. I’ve had several people tell me that’s it’s stopped working when in fact, up close, it’s fully working.

Yep, used loads on several cars, work well and last over a year  Pete
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2014 L405 Autobiography SDV8 4.4 Loire Blue Ebony interior
2011 L322 Vogue SE 4.4 TDV8 Baltic Blue. Parchment over Navy Interior. Sold
2012 L322 Autobiography 5.0 Supercharged Ipanema Sand, Jet Interior. Sold
2002 L322 Vogue 4.4 V8 Epson Green, Ivory over Aspen Interior (Fatty Offroader) Sold
-Click for Project Fatty off roader-

Have you considered using urethane film ?
Plenty of this on eBay.

I've used it on bikes and on car headlights when I found stone chips starting to accumulate.
Can be a bit of a faff to apply.
But take your time and results can be good enough such that the film is hard to spot.

Come to think of it I replaced my high level brake light last year....

Warwick 2011 L322 TDV8 A/b Orkney Grey
2008 Defender 90 XS TDCi Java Black
2002 L322 TD6 Vogue Zambezi Silver (gone but not forgotten)
And one or two bikes - Ok, maybe more than one or two....

Good suggestion TDV8 4.4 2012