I have an oil leak and it looks as though the car is leaking from the sump or bottom end gasket. Has anyone come across this before?

AND on top of that, the car started to develop a hesitant 'jump' when on part throttle, and fully putting the boot in does always clear it, its as though the car is only firing on 3/4 cylinders.
My leads/plugs are fairly new, Magnicors, good plugs etc, any ideas what it may be? The car idles smoothly.