In 60k my K6 wee had the wiring fail between the injectors and was running intermittently on the front cylinder, but got me the 15 miles home.
The headlights cut out while riding at night with my wife on her bike, she lead the way home 5 miles on local roads (I did have side lights).- traced to corrosion in yellow connector behind rad - cleaned and worked fine for the next 30k.
STVA gummed up with road crud and put me at the side of the road, but she restarted and got me to work and home later.
loads of WD40 cleaned it up and never another issue, though I did remove the secondary throttle butterflies
TPS was playing up, but I managed to find a position where it didn't cause issues, but I looking for any NOS unit, but never found anything.
Start switch was playing up and not making a good contact sometimes - commuting bike and it was full of dirt and a bit corroded - was going to replace, but slightly larger failure forced the bikes replacement...
4th gear dog shattered @ 70mph in lane 2, on a bridge with no hard shoulder. - she kept running for me to make a detour to the nearest junction to turn round and come home. all the internal bit knocking around were making a hell of a noise- but I knew from the loss of drive and loud bag the engine was toast but I didn't fancy the 5 mile walk home all I had was 5th & 6th gears, it wouldn't go further down the box.
I can confirm the wee can pull away in 5th if you don't like your clutch to much.
There has been few reported issued with K4-K6 4th gear dogs failing due to fatigue internationally, like 3-4 including mine
I'd still buy another, my bike didn't have a an easy life and was always going to go out in a big way.
Routine maintenance, tyre and chains and sorting frame/engine bar corrosion due to winter commuting and lack of ACF50 and cleaning.
I still miss the bike, nearly 9 years now, and I'm still wanting another.