Defender 110 2.5 Diesel .head gasket

Hi I am an english guy living in Spain, I bought a 1988 L/Rover which needs all types of restoration I am a retired engineer, capable of working on all areas of mechanical repairs but have been frustrated here in Spain having had to replace head gaskets twice, the reason is that the auto product shops have a different system even if you give them the paperwork for the vehicle they dont get it right.I have bought a L/Rover wk/shop manual but it does not give enough detail on the subject.I am a real lover of L/Rovers the first vehicle I drove after passing my test in 1956but only could afford second hand ones of which Ive had three, there is in my book no finer 4x4