1991 Cabriolet Speedometer Cable

speedometer
cabriolet

#1

I’ve struck out looking for a 1991 Cabriolet Speedometer Cable for an automatic transmission. Part number is 171-957-813F. Seems there are plenty for the manual transmissions.
I think it’s the cable. Loud whirring somewhat grinding noise starts around 30 mph and gets worse with acceleration, and then the speedometer goes erratic, bouncing around.
Anybody have experience with what occurs–noise wise–if it’s the speedometer head rather than cable?