Dave,
The only thing I can suggest is the P38 filler/drain plug (metal, with a 1/2" square drive), as these use very similar axles. According to Microcat, the part number is 608246.
P.S., like the comment in your siggy, ref Saab 9-5 - my folks have just bought one, and it's 4" longer than my Disco!!! :lol: