@Dave48, you could use the above kit as Gnasher suggested but then instead of using the final wipe, do a proper lacquer clear coat from a spray can
- just take your time, follow the instructions on the tin,
- spray in lots of thin layers (you do not want any runs) and after final coat give the lacquer several days to cure fully hard.
- then get 2000/3000 grit so to flat it and remove any imperfections
- then buff it with polishing compound to a gloss finish.
@Gnasher I assume my suggestion above should last for years if done right?
Almost there's no need to rub down the lacquer, just ensure the the surface of the lens is clear i.e. properly rubbed down and polished. Then just use quality UV lacquer.
IMHO and if you've not already got the tools/accessories. The best kit is Auto Glym but they
don't give you any lacquer which is barking mad, as it will start discolouring within 6 - 12mths depending on sunlight exposure and the roads you ride on. That said the drill pads for wet/dry and polishing plus the compound is good quality. Good lacquers I've either used or know hold up for 2yrs plus are, Sonax Proflaine or E Tech, I'm sure there's others out there. Sonax isn't cheap, about as much as the Auto Glym kit, but you get what you pay for, about £40ish for a good kit and lacquer, compared to new headlight unit it's a steal.
Obviously it can be even cheaper, i.e. sheets of wet/dry and use a car cutting compound and elbow grease, or you may already have the pads in which case you don't need a kit just the laquer. It's all about the prep get the lens as clear as possible before you lacquer it, if it's quality lacquer 3 - 4 coats applied with either an airbrush or spray can you don't need to rub it down.
Just make sure the lacquer is UV that bit is crucial