I eventually got me Joe in to a mechanic this morning, seemingly every mechanic in the city is booked out fer days in advance.
It was the Thermostat housing that had caused the leak and the cab won't be ready until tomorrow (Fri).
I didn't get a price off him, but I had a look at ebay and they are about Thirty notes to buy, so add in the labour costs and hopefully I'll be out of it fer less than a ton.