I just did this cleaning process a day ago using Windex, a soft cloth, light pressure and a couple of repeats. Just use normal care to remove surface grit/dust beforehand, and don't over-scrub. My results look fine. Recommend that you do not use anything with either solvent or abrasive content when cleaning these gauge faces. FYI, my auxiliary gauges (my Z is a low-VIN, low-mileage MY-1970) are missing what appears to have been glue-faced tape coverings over adjustment ports on the back of the metal instrument housing 'cans'. These ports were part of the OE housing design, allowing the gauge supplier to do final adjustment of the indicator-needle positioning. Once the tape fell off in service, the inside of the gauge became open to back-of-IP dust intrusion. As evidence on my gauges, there's a clearly obvious dust/grit build-up on the surface of the green illuminator bulb hood (which I plan to clean off, first with a computer-type aerosol air-blast spray, followed by Windex on a Q-tip). Also FYI, on one of my aux. gauges the little glued-on white-plastic discs that retain the clear plastic gauge cover had dropped off their peg mounts. This caused the clear-plastic gauge cover to 'lean' on the indicator needle, which in turn caused the needle to rub on and put a light scuff mark on the painted gauge face. Typical, detail-level issues for a 43-year-old car! If there are any places where the industry has really made significant advances since our Z's were designed, it's in materials (esp. plastics) and adhesives. I also used Meguire's plastic polish for the gauge clear-plastic lenses. I used a small buffing attachment on my Dremel, set at lowest rpm. Results were very good. Again, common sense prevails. Don't over-do it. BTW, I've read a few commentaries about the illumination benefits of painting the inside of the metal gauge 'cans' with white paint. FWIW, my gauges housings already have what appears to be a factory-applied (i.e. incomplete and microscopically-thin) coating of white paint.