Sadly the chrome on the reflectors is damaged even when wiping or cleaning. Typically you should only ever clean the reflector with a brush to remove any broken glass (typical from bulbs blowing up) and a micro fibre, using your breathe on it, no water, no chemicals and very gentle cleaning. It's that delicate. Anything else just causes water marks or scratches.
Never used the Halfords chrome aerosol. Personally, think you get what you pay for.
I've been looking at this chrome paint to repair my wheels though. It isn't cheap however, I mean it's seriously expensive. But it looks the part.
https://www.stardustcolors.co.uk/chrome-paint/1229-brush-on-chrome-chrome-paint-using-brush.html?search_query=chrome&results=50#/1000-packaging-100ml
Use Butyl tape in the seal. `Black Silicone` is too general.
There are two types of sealant. Naturally curing, and solvent curing. Solvent curing must not be used, not enough air flow and the sealant won't go hard.
If you have not totally removed the original sealant from the headlight and are re-heating the unit and just wanting to replace some of the material, use Diall Clear sealant from B&Q. It can look like its peeling but it doesn't need air to cure. If you've removed the seal, get Butyl tape, its what the OEM uses (12mm if I remember correctly).