Help - Driving lights have a white coating on inside of glass

I have a pair of Land Rover driving lights (Reed automotive limited) I want to save. Glass fronted, semi-sealed insert with H3 bulb. A strange very even white coating has built up on the inside of the glass lens over 17 years. I have tried thinners (xylene etc), methanol, glass cleaner etc to try and disolve it, but no luck. I managed to poke a small brush through the bulb hole with thinners and clean a small spot in the centre, but it took a lot of scrubbing and lots of thinners and still not able to completely budge it.
I have no scientific explanation of what it could be. Its not pollution from the air (I don't think). Its not on the outside of the glass.
The chrome reflector is ok, nothing on it.
It has been spluttered/sprayed on as if something has been emmitted from the H3 halogen bulb, but that has to be impossible? what could come off a glass bulb?
Does anyone have any idea what chemical I can use to disolve it without damaging the reflector?

Just a quick thought could it be a calcium build up? if any moisture can get in and the heat from the bulb evaporates it it could in theory leave behind any calcium on the lens etc. Try using kettle descaler on a cotton bud or better still if you can remove the light unit lay it on a cloth glass down and pour the solution in, then drain and leave in an airing cupboard to dry for a day or so.

Are you sure they are glass and not plastic ? If plastic you've got no chance.

Put it in the dishwasher,
Or heat it in the oven or with heat gun and separate the lens, investigate further and use a scouring pad or something, then re-seal with silicon sealant

i h ave squirted in gasket cleaner or something like in the past with some success, egt an egg cup full in there and swill it around and leave to soak etc.

Thanks for everyones suggestions. I tried, Xylene, alcohol, ammonia, window cleaner, acid, and much more. Only an abrasive action works and I think if I open them up they will be stuffed. Hence I am now looking for replacement semi-sealed reflectors. Do you think I can find anyone selling (what was the most common headlight for decades) 7" H3 reflectors any more?
Does anyone know where I can buy them from? I hate to throw away the origional Land Rover casing for no good reason whe only the reflectors are milky .