Speedo problems

I have a mechanical speedo in my roadster. When I left home 2 weeks ago it was within 3 mph of my GPS. The last 2 days it is reading 15 sometimes 20 MPH slow. I am guessing the little plastic gears have worn off?? The car is a 32 roadster, 350 trans and has 48,000 miles on it. For the last couple of years, the needle would jump a bit and you could hear a tick, tick, tick. at low speeds, like 20mph and less. It does not do that now. Maybe it was wearing the gears off and now they are almost gone? I am still on the road, 1500 miles away from home so cannot get under it and pull the gears at this time. Your thoughts?

 

cable could be dry..that will cause the square hole in the driven gear to strip...