The tailstock and the off and on switch has been problems for the Jet Mini since it came on the market. Neither have been corrected by Jet, they just keep letting the problem ride. Just one of my reasons I have 2 Deltas and only 1 Jet. When Delta had a problem with the tailstock, the newer models came out with an updated tailstock, when Delta has a problem with their switches they moved them so they did not collect the dust as bad.
If you have a tap and die set, you might try finding a piece of 1/4" thick flat bar steel, with a little work and a file you can make your own "washer/nut". Not easy, but better than nothing.
Marvin