My original solution for brightening up the gauges works well, but they condensate inside due to excessive heat build-up from the extra bulbs, or more powerful bulbs in the case of the sub-dials. I have gotten around this by drilling vent holes in the cases. This completely cures it, but requires disassembly to do so. It's very difficult to remove the bezel on sub-dials so I drilled them upside down and removed the swarf with a magnet; I also used a drill stop! I think LED's would be the answer these days as they are so bright now, and no longer produce the cold light that made me choose incandescent in the first place - and they make a lot less heat of course, so the cases probably wouldn't need venting at all. The amp meter never condensates so no need to vent.
Johnny