Odometer stuck

My odometer recently hit 100,000km, but as it has got to 100,099 it then clicked over to... 100,000 and now only the first digit changes.
A search reveals a not uncommon problem, but the main solution seems to be changing the speedo. Anyone got any other tips as I really want to keep its original speedo

My odometer under reads by 1/3rd but the speed is spot on with my gps. The only solution it seems is to replace the speedo. The gears have probably stripped inside.