Just got car back from painter. Car stayed very moist at times (from wet sanding and washing with windshield out I suspect).

When I cranked car just to verify it still ran, tach was "sticking" at 3,000 or so, but would return to idle after a hard "finger thump" on lens.

Any suggestions on how to make it flow smoothly back to idle and/or zero at "off"?

(I took it apart and no noticeable rust or whatever on what appears to be magnet in center, but the need/spring mechanism is "extremely fragile" appearing, so I don't want to go charging in and ruin it altogether, nor do I want to shoot CRC-56 all over it only to find that you never want to use lubricant such as that due to dust collection, etc......)

You probably have a spec of dust or foreign material on the magnet. You can try to blow it out (gently with lung power, do not use compressed air), or try to clean it off with a toothpick.