Speedo troubles ('84 Spider)

["Simpson, Jr, Joe B." <jbs@domain.elided>]

My speedometer has the shakes.  The needle swings wildly back and forth in
about a 10 or 15 mph swath from the time I start moving until around 30MPH,
when it starts to steady up.  By 40MPH or so it's pretty much steady, and
stays so up to around 60, where it sometimes starts to oscillate again until
at 70-75MPH it's doing a 10-MPH swing again.

I have twice in the past three years had this speedo pulled out and sent to
California for repair, where they charged an arm and a leg to "fix" this
problem (and some stickiness where I had to bump the side of the speedo to
get the needle moving).  The cables were replaced about a year ago.

Does anyone have any advice for me?  If I'm not going to be able to get the
original speedo working correctly, is there an aftermarket add-on kit
available anywhere that would have a small, relatively unobtrusive digital
speed readout unit I could tuck somewhere in the instrument cluster?
Particularly for time-speed-distance rallies, it would be nice to be able to
accurately guage lower speeds.

Thanks...

 -joe

------------------------------