Spark plugs will be ok, repeated use of injector cleaner will dilute the engine oil, one treatment won't harm it, these engines are designed to run on very low octane fuel, they have 8 knock sensors and were made to run on poor fuel because of the areas they are sold in, so it's a waste of time using octane booster... The access panels for the tank are under the rear seat, be very careful taking them off and ensure they are sealed well on fitment.
