Under the seat is a wire connector with all of the wires going into it... Unplug it,and see if it shows any signs of corrosion on any of the pins on either connector... I have the exact same model,and had the exact same issues after I stored it outside uncovered and it rained... The seat safety switch will probably act up next.. You can clean the terminals and pins up and maybe it'll start working right again,or find the correct circuit to the starter, unpin both sides and make a straight connection alleviating the corrosion which is causing the issue... Or cut that wire and run it to a mpmentary switch and then to the starter solenoid and use that for starting...
