Your R1100S has a hydraulically-actuated single-plate dry clutch.
The slave cylinder which pushes the actuation rod through the bell-housing and onto the clutch pack diaphragm under hydraulic pressure from the clutch lever, is an inadequate item sourced by Berlin from a maker of accessories for push-bikes - Magura in Slovakia. As an excuse for employing it, BMW back in the day pleaded lack of space in the area directly in front of the rear wheel - balderdash.
This back-to-front, Morris Mini-Minor-style dry clutch is the bane of many riders lives, owners of this model of boxer. The most common cause of problems with the system, including ever-more effort being required to operate it, is old fluid, ( change the fluid every ten seconds, one owner told me ruefully ) and contamination of the clutch friction plate by leaking fluid caused by a collapsing slave-cylinder bearing.
Investigate at your earliest convenience, please Richard, or run the risk of t-r-o-u-b-l-e.
There's loads of stuff on the web in general and some vids on the Toob for you to watch in horror.
AL in s.e. Spain
