Pull the entire rocker assembly and clean everything thoroughly, especially inside of the rocker shafts. The outside end of each shaft had a plug very similar to a freeze plug. Remove those to make sure that the entire length of the shafts are clean.
Inspect the rocker arms shafts where the rocker arms ride, especially the bottom of the shafts. Lack of oil will severely gall the shafts there.
When you are done cleaning the shafts, you should be able to reuse the end plugs. You may have to expand the end s of the plugs. I use a small ball peen hammer placed in the end of the plug and strike the hammer with another hammer to spread it a bit until it provides some resistance when test fitted in the shaft.
