The steel line under the pushrod cover gets its oil from the rear camshaft bearing. It's not uncommon for that passageway to get sludged up and restrict, or stop oil flow to the rocker shaft altogether. Later model engines had a drilled passage in the block instead of the external line. One of the specialty tool makers (Lisle, maybe?) used to sell a wooden dowel that was a snug fit into the center head bolt hole. Remove the bolt, fill the hole with motor oil, insert the tool, and smack it HARD with a BFH. The hydraulic pressure would blow the crud out of the passages and reestablish oil flow to the rockers. I used a whittled-down piece of a broom stick to do the same thing- - - - -yep, I'm a cheapskate!
Jerry
