I have a basket case  c15 that I have started to rebuild , on getting to the rocker cover I seem to have a hole that does not seem to be on any other Rocker cover I have seen for a C15!

Can anyone advise me?   its on the oil feed side but in the middle of the cover where the rockers meet the push rods! it seems to have been made at the same time as the cover , I have no idea what goes in here  and cant find any parts that would! all I can think is it is another oil feed for the rocker ball and push rods! ?

Any idea’s?