If no one answers your question here, try doing a search in the 'How To' section of the forum - it may have been done by someone at sometime there...
If still no luck, try some Opel O/S forums, I'm sure they'll have the answer to your inquiry above...
You could also try a service centre, I know most local ones here are next to useless, but just maybe you may get lucky...
Oh and BTW welcome to OpelAus.