For Jelco fans, per my post above:
https://www.usaudiomart.com/details/650181966-jelco-tk-850l-12-tonearm/
Pryso, a lot of vintage tonearms have a rubber coupling between the main arm tube, and the rear of the arm tube, where the counterweight rides. These rot from age and should be replaced. Often, original pieces are not available, so work arounds must be made.
Coupling rubbers for the Shure 3009 series are still available. At $85, or so, not cheap for a couple of pieces of rubber, but it is a project that the hobbyist can take on without too much trouble. And the Shure coupling rubbers can be adapted to some other tonearms.