This page shows information different options for the engine oil drain plug.

The plug comes in a version with magnetic center part as shown in the pictures, and one without. The magnet is there to capture metal parts and may indicate severe wear or defects. The plug has a M20x1.5 thread, and a copper or aluminum washer is required. Torque down with 50Nm or 37 FTlbs.

Washer part number 900 123 118 30
Size 22mm ID, 27mm OD.

Plug part number 944.107.197.01, which obviously also fits the 944. Price is approx 18 euro.