Diesel Head Gasket
A new type of head gasket was introduced in 1993. The older one was a mica press with metal inserts, the new variant a steel-aluminum-steel sandwich construction. The old one failed for me at 130,000 km: part of the gasket lining burned out, leaking gases into the coolant as well as the adjacent cylinder. Such failure is not possible with the newer gasket.
If you need to replace it so you have to have the head off, don't forget to do a complete checkup at the same time, including valve adjusters and valve stem seals. With the camshaft housing removed, you can access the small filter in the oil supply of the camshaft. Take care to pull it out carefully and clean it. Also, clean the head and the housing thoroughly, there will be a lot of black gunk. You can now check the turbo, too: it's relatively easily accessible