Big Up for all the Info....
It is def an intermittent issue.... works some times and not other times..
So Ur observation regarding the Slip Ring sounds spot-on.
I have ELSA so will do a little research before attempting DIY fix.
All the other buttons work 100's.
Just as an aside I had the same issue on my Cab and eventually found it was the magnets/switches under the gear lever that needed cleaning. Problem sorted.
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" Love the Sound of a V8....... All Day " *still wish it was a V10*
2002 S8 D2 F/L
H & R Springs, Koni Coil Overs, Dastek Chip, Sport Exhaust, 19" S5 Rims, Solar Sun Roof (Cause we have Sun) and most of the Bells & Whistles.