Be very careful how you get this problem diagnosed. There were some critical (to this problem) changes made to the PD fuel system insofar as the early versions had a fuel/coolant heat exchanger. This was fitted to keep return fuel temperatures within acceptable limits. A failure here could cause your problem.

Later versions deleted this and used an electric lift pump in the tank to recirculate large volumes of fuel back to the tank and also incorporated a thermostatic valve in the plastic "T" attached to the fuel filter canninster. This valve determines the recirculation path and thus regulates fuel temperature.

So, be aware that this is a sophisticated engine and don't jump to conclusions. There is no free fuel at the head/block interface as the flow and return ducts for the unit injectors are drilled separately in the head, higher up.

If the contamination turns out to be lubricating rather than fuel oil, the oil cooler is a favourite failure point on all of these engines.

Check the engine build standard and be absolutely sure of the nature of the contamination before you tear the engine apart. Head gasket failures are not that frequent on 1.9 litre PDs.

659.