I was in at the dealer last month for the 104K timing belt, pump service. They told me that the vehicle needed new plugs and valve adjustment. I had done the spark plugs at home a couple of weeks before, so I asked whether the assessment was based on mileage. They told me that its based upon the engine's Maintenance Minder feature. I'm suspcious about being upsold at the dealer. Is there any way to know when this engine actually needs a valve adjustment? Is there any type of objective diagnostic that can be performed?