the spark is weak, too. so defanately replace the coil instead of trying to repair it. The aircraft i work on with piston engines do this sometimes, always due to a crack in the magneto distributor block, so look closely for cracks or deep burns in the coil housing if you are curious. either way, the coil needs to be replaced.
good idea to check/replace the plugs since a weak/intermittent spark can cause fouling which can lead to uncleanable buildup or damage to the electrodes.
after replacing you should see a noticeable increase in power and gas mileage, too