Thanks for the input guys.
I received the parts kit today, and prepared everything to drop the tranny tomorrow. I love that 6-cylinder S-Class, you can just reach in the top and remove most of the tranny bolts with a big end wrench. I left a couple of bolts in place, and dropped the pan to let it drain overnight.

The fluid in the pan looked okay, just the normal dust.
However, I cut the filter open, and I did find several little pieces of clutch material, about the size of a thumbtack head, in the filter. I assume these are the B3 clutch plates coming apart as others have mentioned.
I'll know more soon, but I have two questions:

1. These little pieces of clutch material should get trapped by the filter, and should not create a clog anywhere else, like in the valve body - yes?
everything was working fine, just the delayed R shift and the rolling/click in R.
So I guess all should be okay, really don't want to test my luck with a valve body teardown.

2. If the B3 friction plates were shelling pieces of material, will the metal spacer plates be okay? I never felt any slipping or harsh engagement.

Tks,
DG