I rebuilt mine to make it stronger for turbo charger, however, when I removed the head I noticed the HG was good as new. I bought my rig with 100,000km so I suspect it might have been changed in that time of the OEM gasket was simply in damn good condition.
Regardless, when I had my engine rebuilt they had to machine about 30thou off the block to get it square. The head pressure tested fine. I believe it's the corners of the block that distort first leading to HG issues. Yes, much of the time you can get away with just a machined or replacement head. However, if you have the funds and the miles are clocking up, a rebuild is a very good idea. Not that anything major needs replacing, more so that the block itself can machine out any irregularities or wear that have happened over time. Another benefit is to ensure the both the head and the block are machined to the required RA (roughness average) which is a grading of how finely machined both mating surfaces are for the HG to get the best seal possible.
Regardless, when I had my engine rebuilt they had to machine about 30thou off the block to get it square. The head pressure tested fine. I believe it's the corners of the block that distort first leading to HG issues. Yes, much of the time you can get away with just a machined or replacement head. However, if you have the funds and the miles are clocking up, a rebuild is a very good idea. Not that anything major needs replacing, more so that the block itself can machine out any irregularities or wear that have happened over time. Another benefit is to ensure the both the head and the block are machined to the required RA (roughness average) which is a grading of how finely machined both mating surfaces are for the HG to get the best seal possible.