Richard covered most of it there, a few years back when we imported alot of these i used to do 2 or 3 of these "head gasket" jobs a week , not one was ever head gasket but cracked or porosity in the castings, from memory new casting with cam was around £400 but that was a couple of years back .Liquid glass worked well on these but was a tempory repair if owner didnt want to spend on them .........."tempory repaired" ones are still running round to this day !!!