The actual cause needs to be established before anything is done. Once this is established, the course of action will be constructive.
If you remember from Shifnal, the stat. had been removed by the previous owner, suggesting that overheating has maybe been a problem before. The oil cooler area has been opened up in the past, (evidence the Red Hylomar sealant), so it would be potentially wasteful of everyone's time to make assumptions without proper diagnosis. I would gladly help, Daz, but 10th/14th April is no good for me, I'm afraid.
A further thought. Dependant on how Kate's car could be taken to Stoke, it might be easier to use my address, which is probably halfway to both addresses. I have a good, private, off road area which could be used, and almost all the tools required, and anyone would be welcome if the date was right. I could even offer overnight accommodation for two males and one female if required, or more if you're prepared to rough it.
And Southport's not too bad a place.