I have had 5 motors that the rectifier was the problem 3 Mercs and 2 Johnrudes. All they had in common was they were the 10-16 amp systems and 1 40amp. In Amtech this was discussed and it has to do with stray currents as this is a unregulated AC system. The stator/rectifier supplies a -AC voltage thru block and this is where packs/switchboxes pick up their bia's voltage. Erratic voltage causes bia's voltage to affect timings in pack/switchbox which effects firing. Also failure can cause a stator to overheat which affects ignition coils, that why the green/blk goo on stators