As an aside, why are you running your motor without load that frequently? Small diesels don't really respond well to that over time.
Over here is comon practice to start the engine every week for 10 to 15 minutes, leave it idle for 2 minutes, then rev it up to 1500 or more, in neutral for a few minutes.
We all do it, and we never had any problems. Mind you most boats get used a lot so this is not needed. Only for boats that are long time stopped.
We know about cylinder glassing, but its a minimal price to pay for not runing the engines. Our diesel is also very good and has algae deterrents from the refinery, and is sold as marine diesel.