Transmission fluid filter question

I bought an S8 that has had less than 500 miles put on it in 2004, mostly sitting on the dealer's lot. It has 22,000 miles total.
I've read that the transmission fluid and filter become a problem on S8 and A8s. Should it be done now, irrespective of miles, due to the years that have gone by, or when do most of you have yours done?
Same question as to differential gear oiling? I tend to have my car differential drained and renewed about every 4 years normally, but I've never owned a Quattro before, so I don't know what the norm is. I don't see either of these on the scheduled maintenance list that I downloaded, at all.
Same question I guess as to the cam belt, and the serpentine belt.
Good resources for all of this??
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