Well done Martin.
Bear in mind that when doing any diagnostic work, the cost of replacing service items can always be justified whether it's the cause or not. There used to be a company called "Home Tune" and they would always do plugs, points, condenser, air filter etc before any other work (they may even still be in business but I've not seen them for a long time). Even an oil change can have a marked affect on a modern engine.
Regards,
Bryan.