Speedometer broke. For the second time.

Directional forces from the cable is what wears speedometers. Early models have simple collector nut providing very little alignment support. Later models have improved plastic sleeve like connector about a inch long to better align the cable and sheathe but... everything wears out eventually no matter how well it is designed.
Tiny bronze bushings and very little clearance between the speedometers rotating parts. Wear causes one to contact another. I have had pictures to share in the past that show scared on the outside of the drum shaped part, and closeup pics of the egg shaped bushing bores that caused it too.
All we can do is clean the crud from square input port so there isn't inward pressure, and align the cable and sheathe as centered as possible.
Since your collector nut and flange beneath is the only alignment support, to snug that nut is better than leaving it loose.
The cost to rebuild is relative to the availability and cost of replacement parts (those tiny naval bronze bushings, etc..). Their inventories of good used parts are surely depleted today.