it ended up being a core plug in the block behind the timing cover, it was leaking straight ito the sump

If it was a core plug water would leak out not in to oil I would expect so could be head gasket or oil cooler maybe I'm not sure on that set up

Hello Andrew,
check the oil cooler for internal leakage. When the engine is hot you will have pressure in the cooling system. The water or vapor will be pressed in the oil circuit as long the engine is hot. Next check would be the cylinderhead gasket.
Kind regards
Andreas

Hi Andrew,
The Kubota is a good engine, but this could be a few different issues. Combilift have a dedicated Technical Team in the UK. If you still need support, you can complete a quick technical support form at the bottom of the main combilift.com web site or direct link https://warranty.combilift.net/technical-support-form/. The form only asks for the minimal info so the team can quickly help you. There is no login required and no charge for this support.

The UK Team will be back to you quickly. Hope you get sorted quickly.