[Britwrench]

On the other hand, the selling dealer may not have had to change the oil if the service history stated that maintenance was up to date and an oil service was not required.

The in-hex drain plug can be damaged, usually a new drain plug (and crush washer) is all that is required.
It is the same part number as a 944/928 cam housing plug.

If you are changing the oil yourself, always use a good quality 3/8" drive hex socket and torque the plug to the factory setting.