Plate between block and timing gear housing leaks when engine cranked:
But, not when the raw water pump rear cover is removed:
It looks like the leak is only there when the system is pressurised,and the oil seems to come, not from the rear of the pump cover but from between the engine block and the front plate.
The parts explosion:
It looks like there are 2 missing bolts securing the plate to the block.
(Jan 2018 – NB. I think back in 2016 I purchassed and fitted these 2 bolts and that cured the leak. Now the engine has been rebuilt the leak is back. Is it possible that when it was rebuilt these 2 bolts have been again left off again? It would be relatively easy to put all the outside bolts in and miss these 2 inner ones?)
This picture show a new plate being held up in front of the gears of the gears just to give an idea of what is behind: