Screw on the Agregat carrier spins

Hi

With me, a screw goes crazy (M12, 98, 10.9). It's the one sitting right next to the right crossbar.

The great flex and sweat action I would like to pinch!

The thought. Drill on M14, cut threads and take larger screw.

Drills and the threaded section I get here at a special company... Where can I get the screw? M14, 98 - 100 mm long and strength 10.9?

Audi only has up to M12 (according to the part fuzzis), AET (car parts dealer) have only up to strength 8.8. A large Reutlinger hardware dealer has only 8.8 and it is too much to get a 10.9.

1. Question
Where do I get the screw?

2. Question
Who's done this before? What else should I look for!?

Thank you!

Frank