Soft Aluminium casting?
Part of the issue I had when torquing the head initially was the fear of stripping the threads on the studs, when tightening down it never felt quite right as if something was giving. I assumed this was the head studs on the threads but on closer inspection I'm wondering if the head had gone soft (is that the correct term?) with a straight edge you can see indents where the washers have pulled down into the head. Was the 1st failure partly down to the head not being tightened correctly.
