Its easy enough to remove the rocker arm assembly and clean out the inside of the rocker arm shafts to restore oil to all of the rocker arms. While it is apart, you can check for excessive scoring on the rocker shafts.
As far as sticking valves, that can refer to where the valves contact the seats. It can be caused be running the engine on old fuel loaded with varnish.
Don't give up yet. You can't kill these engines. Yours seems to be just temporarily disabled.
Carl
