[Farrell In Vancouver]

I would remove and bench test the starter. While you have it out check the mounting surfaces to see the starter and flywheel surfaces are clean, as every bit of ground will help.
The three mounting bolts should be cleaned up as well. If you can get the starter to jump on the bench with a 12 volt, you can probably assume your six volt is toast and needs to be swapped out. One thing the starter switches hate is low voltage and will cause the contacts to weld solid if strained enough.
I think you're close, keep poking!