Hi Mike,
Well, when I drove yesterday a boring stretch of motorway I pondered a bit about your problem. If you rule out the air condition charcoal filter you may in effect end on the cluster needles. Those are cold cathodic lights and as such do not give a continuous light as standard glow bulbs. But I do not believe they emit a significant amount of UV-light. At least not more than natural UV from the sun. It may be more the frequency that puts a load on your eyes. This was a common problem in offices before the computer displays were able to reach frequencies above 75 Hertz.
If so you do have 2 options. Either you can have the cluster modified which will be both onerous and time consuming. Or you may opt for reducing the contrast.
If it was for me I'd go that way. Have you ever seen how window tinters do their job? They do in most cases not tint the glass but apply a thin film of special plastic to it. Those plastics are available in a wide range of colors and degrees of shading. This goes from 5% to 90% tint. All colors are available too. AND those do reduce the amount of UV considerably.
What I mean is: Do have such a film applied to your instrument cluster. For myself I'd choose a grayish or geenish tint of 30-40% shading for a start. I'd also have it applied only to the upper part of the display where the needle gauges are situated. In the bottom the warning lights do not need a shading. Also the brightness sensor is located in the bottom row, at least on my LS400. This sensor can be seen when direct sunlight shines on the display. Do not cover it.
The cost for this will be more or less neglectable, maybe 30-40 Euros if you haave it done professionally. Maybe half of it if you do it yourself but I do not recommend this unless you have already experience with this procedure.
A big advantage is that you can remove the film, without tolls and without damaging the cluster or leaving residues.
If this still doesn't work we can still exchange the cars. Interested in a LS400 with 30.000 miles? :winky:
Alain