Series 3, petrol 2286 cc engine.

I have a coolant leek which is coming from the left side of the engine at the rear just under the manifold, there is a manufactured whole in the engine block - circular about 2" in diameter with two lugs at 3 & 9 oclock
theres no screw thead

ive checked the military manual i have & thought it was the cylinder block drain tap but alas its not (infact its about 12" behind it & 3" above)

Ive added the best pics i cud take - the last one shows the left side of the block, the hole in question is about half way done on far right edge.

please help as if i fill the rad with water it pours out of this hole just as quick