Well its working again. As the gasket had cause the last failure I decided to replace it. I also took the chance to replace the 4 bolts that hold the head to the barrel as 1 or 2 had damage on the threads. Also fitted a new base gasket and new seals at the end of the pushrod tubes as they were leaking a little oil. There seems to be signs the copper cylinder head gasket has leaked in the past and its just been done up tighter to get it going again. There is a indentation into the head that is from the copper gasket but only near 2 of the 4 bolts that hold the head to barrel. The head also shows some squashing of the metal on the top area of two of the bolts so we used 2 washers to pack it out more otherwise the bolts would tighten against the thread in the barrel rather than putting pressure on the head against the barrel. On the last two outings on the bike I had lost 2 nuts that hold on pushrod inspection/rocker cover so I bought some new ones from Jampot Spares and then drilled and lockwired them in.