I recently picked up a second hand K3, working but needing a little TLC. I guess it's a few years old as the power is a whopping 2100 watts - not that it appears to have any more suck than my 900 watt K1!
Anyway I soon discovered that the telecopic tube is not closing fully. On removing the cover I found that the mains flex was bunching up on one side and jamming as the tubes were pushed together. So I straightened out the flex. Also it seemed to be coated in something like french chalk, so I put some talcum powder on and now it seems to be working properly.
However, I also found a little spring rattling around loose inside there as well and I can't work out where it came from. It's a U shaped clip with an overall length of about 20mm and a width of 4mm.