3) The knob on top was missing so I am assuming you could replace it with a similar stove/bbq knob? Has anyone found something suitable? I just adjusted the knob with plyers during testing.
I may be wrong but that looks exactly like a 'D' shaft or grub/set screw. Very common on hifi, instruments and electrical/electronics equipment. You get a knob with a round socket and little grub screw to hold it.
That and the split shaft spline are the most common for rotary switches and potentiometers, those are push on with a matching spline.
If anything the difficulty more would be getting something that looked appropriate for the mower. Depending how close to original you want it, if you can find anyone that knows or has pics.
Just google set/grub screw konb or d shaft knob, plenty of affordable ones floating around, Jaycar, Altronics, RS or similar local electronics shop should have something off the shelf that will work, as I said some may look a bit weird on the mower though, might want a more 'industrial' looking one of a bigger size.
