oil leak

[bobfish45]

When changing the gearbox last week there was a bit of oil over the starter and down that rear quarter of the engine. It had actually seeped between the bellhousing and block. It was wet up as high as the head though didn't appear to be rocker cover. I've cleaned it all off and left the engine on 1500 revs for a while, had a look down the back with a mirror but can't see anything leaking. Tandem pump is clean as is where injector lead exits, any ideas boys?