I had a Pontiac tachometer repaired at APT Speedometer in Bloomington with good results. I also had them restore the gauges for a couple different motorcycles and was very happy with them - one set of gauges was literally a pile of parts in a box, and they brought it back to NOS condition.
Address: 9632 Humboldt Ave S, Minneapolis, MN 55431
Phone: (952) 881-7095
Their website was
http://www.gaugeguys.com, but it's not working now...I don't know if they just let their license expire or what. I guess calling them on the phone is the best bet.