Good point on the valvecover but it appears to be tapping wihout the cover also . As far as the shaft impeding the flow , that won't happen . What happens is the rockers don't get oil to the high stress area where it needs it. It would be a good idea to pull the rockers and shaft and look for galling ?
I don't know if the hughes rocker is an alum body on the steel shaft , bushed , or full roller on the shaft ???