Too much $$ for a speedo, Sorry to
hear about your bad mechanic.
The reason I asked about the cable outer
or Shieth, is that the lube in the old cable
is likely dried up and needs to be re-lubed,
but don't use grease, it's too thick, not now
in the summer, but in the winter it will make
the speedo cable wind up and whip the speedo
needle.
You need some light oil, or WD-40 like lube to
loosten the old lube up, you might even find
out what a speedo shop would use.
Hope you get this worked out with no more $$
out of your pocket
Good Luck
Wild