My C5 has one just like that, no oil though,
Relax - It's just a cross drill oil hole used to connect the hole in the base of the cylinder with the hole that goes THROUGH the cylinder to oil the top end. After the passages are connected, the outside is plugged. That's what you are seeing. It ain't no thaing!
If you open the picture in new tab and enlarge (+) the picture, you will see oil coming out of it - what do you make of that ?
This hole is for the water drainage around the plug. Try putting some water on to the plug and see it for yourself.
SSR is right, it's a water drain.
You mean water from spark plug on the left side of engine drains through this hole on the right side ?
Singh JI, all the UCE engine have only one water drain on the RH side weather its domestic or export C5. The one and only primary plug you have does not have a drain hole like on RH side. There is a gap between the fins and the block near the LH side head bolt(next to primary plug) Water does not collect there.While on Rh side where there is a secondary plug or in export models just a deep cavity. On RH side the fins have metal to metal contact with the head without any gap(Rh side of head is wider then LH side) so they have intentionally had a drain hole because of the cavity form due to the head design.The oil/moisture you see is from the barrel /head gasket. Tighten the head or replace the metal gasket if you dont want to see any oil there.