I have an oil leak coming from the small domed unit down the back of the engine block. Is this an easy fix or not.
That's the crankcase breather pod, there is a mesh filter inside which often gets blocked. Access to remove it isn't the best, and it's quite a tight fit in the block, especially a new one. You'll need to prise it away from the block without damaging the mating surface. You can clean the mesh, some people remove it altogether, some re-fit the old pod and use gasket sealant, some fit a new pod without sealant.