I had a good look at my valve cover and its surrounds. I discovered that you cant re-torque the cover bolts with out first removing the injector tubes. That's not gunna happen any time soon. But with a good light I think that I have discovered the source of my oil leak. I'm pretty sure that its the rear (number 4) injector seal. I don't know if its very clear in the pictures but I've put them in anyway. Looks like its a new valve cover for me.
injector 4.jpeg
injector 2.jpeg