It's generally exhaust tappet and lobe on no1 cylinder that go, for some reason it doesn't seem to get as much oil as the others, just by turning the engine over by hand with the tappets removed, it's plain to see that only a small amount of oil is getting through compared to the other tappet bores. Maybe 2 oilway bores dont quite meet perfectly or something...I'd take a close look but I only noticed once the head was screwed down, while checking that the oil pump was full and working. Next time the head is off I'll try and take a closer look - or maybe cut an old head in half to find out how the oil flows around it, and if anything can be done.