Largiader says interchangeable. https://forums.bmwmoa.org/showthread.php?78245-Does-a-R100R-Use-the-Same-Seat-as-a-R80-R100GS
I guess best to see if you can try to swop someone's seat over.
Hi,
I can confirm that the GS dual seat does indeed fit the R100R
Thanks to helpful advice, I just went ahead and bought one.
I’m pleased with the subtle increase in height. Bars feel a fraction lower, foot controls more comfortable to use
And possibly less contact between inlet and right leg.