Did you look for crud on the inside of replacement shaft? (Sorry, have to ask.)
Is there excess clearance between the rockers and the shaft? This will prevent oil from maintaining oil pressure all the way to the end of the shaft. When this happens you can usually see excess oil dribbling out at the bottom of the rocker instead of out of the hole in the top.
Try to dial up the RPMs a bit with the idle stop screw to see if the oil comes out of the holes in the top of the rockers.
Carl
