So in true gullible home mechanic style I was inspired by TomL and RichTea to clean the rad... all I can think is that the rad on K13 is easier to access than the one on a K12....
What a b*#*$d of a job!... Tom absolutely no way you can pull a fan on a 12 without removing all the rad fixings, plus even then the top right (as you're sat on the bike) screw for the fan housing is flush to the headers and even with rad mounts unclipped, if you're not undoing the plumbing forward movement is barely a cm making it ultra hard to access.
What a sod of a job, still all done and reassembled... the bike will need to blow up before I do that again.
Also spotted some fab 'chimp DIY' from a previous owner... There's what looks like a plastic expansion tank at the top of the rad that connects to the water pump feed that I think should be secured with some form of large Spring clip... Looks like someone broke it in the past and just poked the broken bits in to the gap in the cap... No idea if it's critical but all seems to run well.
Remind me to ignore you guys more