The Finest Year ('85) and earlier K100 has the first design sprag clutch - and it's problematical if the technique I describe will help - but easy and cheap to try. It's also possible that your sprag clutch has accumulated moisture causing rust of the components (one of the problems with short winter rides) - and in this case disassembly is probably the only answer. (BMW changed the design in early '85 due to exactly this problem - the new design helped but did not entirely 'cure' the problem - it still occurs once in a while on K engines).
OK - the process I've used with success (and it has worked about 60% of the time for other people - no guarantees)
Go to a local auto parts store and look for an oil additive which describes itself as a 'detergent' - we do NOT want any oil thickeners (like STP) - we want something that says "Cleans rings, hydraulic lifters, etc.." "safe to use in your oil" - we are not looking for an engine 'flush' - we're looking for a very specific oil detergent additive.
I personally have had very good luck through the years with a product called CD-2 Oil Detergent. Paul Glaves and others have used a product called Rislone with success.
With CD-2, (make sure it is the 'detergent') - I added 1/2 a can to a fresh change of oil - and then ran it for 500 miles and then changed the oil. Any of the detergent additives tend to dilute the oil, so I don't like to make it part of the bikes regular diet. With CD-2, you could add it even if you were full up on oil - the can isn't very large. Rislone comes in a quart, so adding even 1/2 of it might require lowering your oil level somehow.
The brand of oil you use may also have some effect on this behavior.. I find I've had good results with Castrol RX-Super 15-40 fleet oil.. I'm sure that any quality oil will help avoid the problem, as will longer rides in the winter to allow the oil to come up to temperature and burn off moisture.