Thanks guys. Decided to back out of the sale. A new head is £950. Yes the chance is low and it was probably the studs leaking but other factors put me off. It had a 920 kit (which I always have lusted for) but it was clear he had tried to fix the leak and not cured it. He had had the head skimmed at a local engineers. I asked how much they took off and he didn't know. Nice bike but had no history so I will look for another. Cheers.