[Synchro909]

I've never replaced plugs as often as manufacturers recommend - no need to for obvious reasons. Points: rarely, when there is virtually no tungsten left on them and as for oil, Do you have a filter? Do you use detergent oil? If yes to both, I change at about 2,000 miles for short (under 200 miles at a time) running and for long trips, (over say, 1,000 miles) I watch my speedo, oil pressure (I run a pressurised middle main bearing) and temperature. When the oil is at the end of its life, the pressure starts to drop for a given speed and temp. With the cheapest of cheap oil, that happens at about 3,500-4,000 miles.