Help from you Tinker Types

[PbFut]

My truck likes to mess with me. As soon as I get it “done” it will find something else to mess with me.
I have an original Stewart Warner Step Up/Down Speedo cable speed corrector. It makes the Speedo dead on to my GPS speed test and appears to be from the 70's aftermarket.
The other day, out of the blue, the speedo started a death jump. Minutes later no speedo. Did the cable test with a drill. All good. Went on to the speed correction device and proved to be free wheeling.
A simple device it looks like a model of a 1 speed transmission. Two shafts with tiny pressed on gears and a intermediate stepper gear. The gear on the slave shaft that is presses on has come loose and will not hold to the shaft.
As far as I know, no longer produced and no parts I need to somehow affix this gear to the slave shaft. What do you recommend?
Solder
JB Weld
Foil and tap back on
Other Ideas Appreciated.