Paul,
I have a 74 TR6, but no idea if anything is original. For the TR3 I'm working on (not as often as I'd like), I carefully took my (1961 TR4) gauges apart, and cleaned them. I used a fine rubbing compound to carefully clean the face plates, avoiding the white as much as possibe. You'd be amazed how good they look after doing that. Pictures included of lens, before cleaning and TR6 speed-o.
How's this for pitiful? I take pen and paper out to the garage because I know I can't remember the part numbers long enough to get back to my computer. When I get out there, I can't read the numbers -even with my glasses off. So I have to take a picture and zoom in. I'll be 47.5 next month -but I still have the attention span of a 2yr old.
If my old gauges work half as good as they look, I'll be satisfied. I tested the speed/tach with drills and cable end, and the fuel with proper sending unit, but don't know how to check the oil pressure, and haven't gotten around to testing the sending unit/temp gauge.
Jer