Race cars in
Join Date: Oct 2007
Location: South Africa
That is the strengthening mount point for the water bypass channel from the thermostat back to the block water inlet.
Oil should not be be seeping out from there - The bolt that should go in there is quite short. I think someone screwed a too long bolt in there and might have cut into the block wall, into a oil channel. To be honest The water bypass channel is quite strong enough to carry its own weight. I'd clean out that hole as properly as possible and seal it with Pratley's Steel. You can try it without removing the exhaust, or you might need to remove it, to remove the carrier stub