The strip of metal near the top left corner of the replacement cover is positioned over another set of holes. I suspect these are nominally the inlet, with the strip of metal acting as a shield preventing oil running down the walls from trickling in. The holes at the bottom draining any oil mist converted to liquid drops by the wire wool.

If you have the problem and can't lay your hands on one of these alternative covers it seems to me you could weld a plate over the hole and drill your own holes along the bottom, although I'd remove the wire wool first, drill the holes in the right-hand half of the cover and be sure I had got all the swarf out, replace the wire wool, cut the plate to size, drill that before welding (to keep swarf out of the cover), then weld it to the cover. Or maybe weld a plate over the hole leaving just a narrow slot at the bottom.