Nasty surprise

[BSM]

Thanks for all of the above input once again. After demystifying the problem to be tackled the Locknstitch bits were purchased from a very helpful agent in Mackay (QLD-Aust.) and the work began. Few images attached for those interested. You were correct Gordon. After removing more paint the problem grew to approx 4inchs. Some magnaflux chemical was purchased and after a few trys (alias learning curve) I finally got a result. Turns out it helped to remove the normally rough skin surface in the vicinity of the crack. First pic is the result. This was followed with a centre punch to make it more pronounced.
The other images show a few of the steps with the last being the end result. Pin edges can be peined or done with a 2mm pin punch which was the final choice. Engine now back in as of yesterday and all being well the leak will be a thing of the past. Rod