I have some second hand information.
When I was looking for a sport touring bike big enough for my wife and I to ride on, a friend who is a very experienced rider kept recommending I go ride a K75. He and his wife had one and they took many long tours on it. He claims it is one of the best bikes he ever owned......and he has been riding a very long time. Currently they own a Triumph Bonneville and the just got back from a 3,000 mile trip.
There are some really nasty, abused, beat up bikes for sale, and also some very nice ones.
https://cincinnati.craigslist.org/mcy/d/ft-mitchell-1990-bmw-k75-low-miles/69...https://cincinnati.craigslist.org/mcy/d/melbourne-bmw-k75t-1987-blue-hard-bag...For some reason I just could not convince myself I needed a 30 year old motorcycle to take long rides on, and I bought a 2016 BMW F800GT instead. It is a great motorcycle so far, the only issue that is bothersome is the amount of wind noise in my helmet from the air coming off the stock windscreen. Several of us are trying aftermarket windshields, and I believe we have found the ones that work.