There was a TSB on some engines with the block not being properly machined causing oil leakage from the crank seal.
Vocky, Had a little look at my spare motor (how handy) and when I take the top off the filter housing the body piece comes with it. Ideal for swapping the cooler seals but how do I separate the two to change the filter? Is there an electronic haynes style manual for this motor? It'd be dead handy for reference.
Ephid0r, thanks for your original help, it gave me hope and some initial guidance that was very much required.