My experience with this engine is that GOOD GAUGES ARE ESSENTIAL and can catch small problems before they become big problems. The Ford idiot lights are useless. Before buying a 6.0 one needs to know the temperature delta on the EOT and ECT. By keeping this at <15 degrees, most of the expensive repair issues can be avoided. Blown EGR coolers and head gaskets are a direct result of a plugged oil cooler and the only way to monitor this is by using good gauges.
The STC fitting on the oil cooler is known to be a weak point and can cause hot no-start issues but an updated part is available and is not that expensive to replace.
The other one is the fuel pressure that the ECU does not monitor but can be easily checked by an external pressure gauge.
If you know the weak points and check them before buying you'll have a workhorse of an engine.