My experience has been that the PO had 5W instrument cluster general illumination bulbs where there should have been 3W (194 style bulbs). The result was seriously melted and deformed prisms adjacent to the bulbs and some melting/warping of the white plastic that surrounds the bulb. The latter is often evidenced by light leaking over to the turn signal light area so that they appear partially on all the time.
My solution was to find a good used instrument cluster with good prisms and good white plastic surrounds (eBay) and then stay away from 5W bulbs.
I have since done some experimenting with lower wattage LEDs, with mixed results. One attempt seemed promising, but the illumination angle of 35 degrees was not adequate to reach the prism, which is not straight ahead of the bulb (I think it is higher). This attempt using LEDs from
www.superbrightleds.com (30 mA at 12V, so very low wattage)
Another attempt was with an SMT surround light LED from
www.ledlight.com. These put out 1.5W, which is a lot for an LED in this usage. Unfortunately, I tried these not knowing that my prisms were already melted. When I get around to it, I'm going to try again with the new cluster shell and prisms.
General conclusion to date: the prism and light tunnel design sucks and there is not a whole lot you can do about it.