It’s often one step forwards and two steps back on this type of project. I had the rear engine cover and heater fitted and all piped up, and thought it would be prudent to check for leaks. So I ran the engine up to temperature. I then found that there was water vapour and drips coming out of the engine breather tube. Sure enough, there was definitely water in the oil. The cylinder head gasket had obviously failed. This had been fine up until now, as far as I know. So nothing else for it but to take the rear panel back off and the radiator, and then remove the cylinder head. The gasket does look a bit suspect in one area, so that would explain the leak. I have the spare cylinder head if I need it, and also a new gasket. So I ordered up some new bolts. The components will be cleaned up and then reassembly can begin.