the hex "nut" is not plastic... it's metal and steel IIRC. And it's an extension "arm".
Issue more than likely is your tool; they strip easily to prevent damage to the headlight unit. Try using a long nut driver or socket w/ extension (5mm rings a bell). Or you can always pop out entire headlight pod adjust w/ it removed as opposed to thru the portal.
If it was that discernible and you have never noticed before, I'd also check the bulbs to ensure all are functioning. In a 986 halogen system the hi / low / fog bulbs are all H7 (again IIRC).
Good luck
