The first place I’d look is where the high voltage leads contact the motor, especially where they drag across screws or castings during speed changes. And a wire may look OK at first glance, but if the insulation has once broken down to allow a spark to go to ground, there will be a tiny hole burned through the insulation.

Also check everywhere that the wire is clamped or secured; I had a motor with intermittent spark failure that turned out to be a thinned portion of insulation under a clamp.

Don’t think the primary side carries enough voltage to cause a shock, but I’ve no idea what the primary voltages are.