Oswald - When you tested the rocker oil tube piece, did you block the hole on the inside of the collar that rides on the rocker shafts? That's where the oil transitions from the feed tube to the shafts and that should be unrestricted. The pinch off of the tube beyond where it feeds oil through the collar should restrict flow out that tube. To test if its actually restricting anything, the hole in the collar needs to be closed off.
Should be able to do that with your finger inside the collar while you blow through the feed tube. No air flow or restricted air flow would be the sign that the pinch off is doing it's job.
