Progress so far today:
Finally decided to 'bite the bullet' and attack the inner reflector cover sidelight area with my Dremel!
The area where the LEDs are on the side of the lamp are the widest part - needed opening up about 0.5mm all round so I just carefully used a small drum sander attachment on a slow speed and worked my way round, checking the clearance as I went.
The inner reflector probably doesn't look a lot different:
I've only wiped around it with a very fine microfibre towel. It's made no impression on the marks above the xenon bulb holder, but a fair bit of muck did come off on the towel so I'm happy it's as clean as it can be.
The inner reflector cover I decided not to polish - there's a lot of silvery finish edging to it and held up to the light it's pretty awful quality finish that you can see through. I was concerned polishing the lens would damage the silver finish very easily, so I just used some Autoglym Fast Glass on it to remove dirt.
ETA - don't attack this part with anything other than water and a microfibre rag! The finish is VERY easy to remove!
The xenon bulbs were replaced with new old stock (allegedly) bought off ebay when I bought the car - they appear genuine, although don't seem to have some marks down the socket end that some sellers claim only OEM bulbs have. I suspect these are actually quite old bulbs in terms of shelf time, as the light up time is very similar to the original bulbs that came out 4 years ago! Takes almost 30 seconds for them to reach full brightness. They don't appear to have aged much anyway, so I'm happy with them. The salts still look an acceptable colour.
The main beam support/flash bulb is a Philips X-Treme Vision +100% bulb - they work well enough and a reasonable xenon colour match
their life is about half that of a stock bulb, as you'd expect when they burn twice as bright, but for the application that's fine.
And now with the inner reflector carefully put back on and all the clips engaged, and bulbs refitted:
The sidelight LED sits nice and central in the housing, so that's good. It's designed to take a very lightweight filament bulb so I was concerned it would 'hang' a bit in the housing. A tip for anyone doing similar - DO NOT be tempted to try and tweak the 2 plastic barbs that hold the bulb holder in situ to try and get them to grip a bit better. They just snap......you can guess how I've found that out
Just spoken to TPS and the wiring for the sidelight bulb is available from stock in Milton Keynes (8 on the shelf!) so I've ordered one to replace the one I've snapped and if they're more pliable I will order one for the other side. It comes as a wiring kit for the headlight but I'm hoping I can just persuade the wires out the back of the bulb holder and just change the plastic part. I'm not convinced until I see the part that it's possible to change in situ if it comes with all the wiring back to the plug!
I now need to attack the main lens with the polisher so that's ready to go back on the car when I collect the new clips tomorrow, plus hopefully the wiring. I'll try and grab a pic of it reinstalled with the old one for comparison. Will be very interesting to see if there's enough light coming out of the sidelight now to illuminate the main reflector, which I think is the purpose of the cutout in the sidelight reflector. The old filament bulbs didn't stand a chance of doing that, they're so weedy!