K100RS - I disagree with most of the negative comments. I had two 1985 K100RS's, both bought new in 1985, one of them on a bike tour of Germany. I had intended to sell one of the bikes, but I liked them so much I kept both, until the first one was totaled in a wreck in 1987. The second one? I kept it as my only bike for 30 years! (With a 10-year layoff during children.)
I had customized the bike to eliminate some annoyances, so here is my short list of annoyances and what I did about them.
1. vibration causing heat shield to vibrate noisely, and eventually break the bolts. Replaced the stock bolts with bigger ones, basically. Not as pretty. but worked for 25+ years.
2. Handlebar grips too small - replaced with fatter Gold Bond grips.
3. Seat - replaced with Corbin seat. Everyone has one problem or other with almost every stock bike seat.
4. Heat from engine at slow speed (here's a real annoyance, especially living in Phoenix. ) - installed aftermarket fairing panels that sealed off the area under my knees.
5. Vibration - like every 4 cylinder I've ridden, it's buzzy at some speeds, very smooth at others. I avoided the buzzy RPM's. I think the K1300s is similar, but a small bit worse in the handlebars. (K1300s is MUCh better in the footpegs. I added grip puppies on the K1300s as I wanted to keep the stock warmers).
6. Gas tank heat. Apparently the fuel pump on a K100 recirculates a bit of fuel back from the engine to the gas tank. Or the heat just rises into the tank. Whatever, but on a hot day (100+F) that tank can get so hot my thighs were red after a ride. I wanted side panels on the tank, but never got any, so I just avoided pressing legs against the tank in slow, hot conditions.
7. Smoking at start up. SO annoying, an why didn't the engineers just flip the design so the heads were on the right side? MY solution was pretty simple. I *always* used the centerstand when stopped. No more problem, plus I didn't have to worry about the side stand sinking into hot asphalt.
After 30 years I didn't really trust the K100 on long trips anymore. It had died on me twice around town for failed fuel pump and once due to a broken ground wire. I decided to splurge on a new K1300gt and went to the dealer for a test ride. And found out they hadn't imported that model for years. So thought about a K1600, but they had no demos at that time. But there was this gorgeous K1300s MS... One test ride was all it took. I eventually sold the 1985 K100RS to the mechanic who worked on it for years for $1000. He had a primer red K100 tank in his garage already to replace the primer white one I had on. (Had to replace gas tank, all rubber bits, fuel injectors and a bunch of other stuff after letting the bike sit 10 years.)
In the follow pictures, you can see some of the mods I discussed above, plus rubber gaiters on the fork seals.