My tach needle is suddenly very slow to move. Revving the engine causes it to rise very slowly and it takes several seconds to return to zero when the ignition is shut off. It was rebuilt several years ago and worked fine until this week. A quick check of the wiring at the coil didn't turn up any problems. Any ideas?

Thats an odd one ,normal fault is the damping goes out and the needle over compensates
and bounces all around with rpm range.
Appears it could be a mechanical issue as it is slow to return with engine shutdown ,if you are brave enough to remove the bezel you may be able to free it up,cheers

sounds like the needle is gummed up
Sounds like a clean and lube may get you up and running