I might add a little to this, use it if you want.
Failure of thes motors is a combinatiuon of a few things.
Weak intercoolers, as many have seen they have cracks in them and leak. Good sign of a cracked cooler is black oil marks on the cooler its self.
Cracked cooler, releases boost. Computer realise that boost is lower then needed and ups the boost.
Computer thinks the motor has X amount of boost but really has -X boost, more fuel is added do to the boost increase, but the extra boost is not really there. leading to high egts and holes in pistons .
This is how I understand it works. I may be a little off the mark. This may be more so in earlier zd's with poor computer control.
Intercoolers are a common problem, and i know upto at least series 4 they stilll crack. I can't comment of after that model because i have not looked at one.
I am going to do these mods to the father in laws series 4 zd.
Possibly, somethinkg about catch cans to might be good.