... it must be a universal socket 10mm works like a charm.

Thanks for this. After spending 2 hours trying to get a grip on that nut, I took your advice and bought a miniature swivel socket 1/4 drive 10MM. I paid $6.95. I only removed the vacuum lines in the way. Put several 1/4" extensions together to make a reach of about 16 inches. Leaned into it to keep a bite and turned the wrench. 10 seconds! The right tool sure makes the job easier. Thanks for the tip.