Folks here have been especially helpful and kind enough to help me with a couple of queries, so I thought I might give a little back by way of advice.
I had the ubiquitous seized cooling/radiator fan on a K100, probably something to do with the 'bike hanging around for not too short of two decades. I had the radiator off and the thing was solid, with the whole motor assembly wanting to turn in the plastic shroud, rather than the fan. Apparently a common issue.
Left it to soak for a couple of days in good old WD40, but still no joy with it turning.
Not wanting to be beaten by an inanimate piece of gubbins, I decided to give it one last go last night.
Overcome the genius design of two wholly inadequate strap-ons captive fittings holding fan to rad at the bottom. A sharp 8mm drill bit sorts them right out.
Fan off, I applied liberal quantities of Penetrant fluid into the fan motor.
Fix the thing in a vice and give it a wee judicious wallop on the fan-end of the shaft, not the full Jeff Capes, then flip it over, electrickery side up. (Good time to inspect/fix the the solder joints. Mine were all good)
Get a good load of fluid into the motor, and around the springy press fit washer holding the end of the shaft. It can be popped off as well.
Stick a rounded off piece of steel rod/old cut bolt/anything that gives a straight, yet blunt protuberance in ones' cordless drill and set phasers to 'Hammer action', rather than drill. Most drills have this.
Press hard against any metal surface on the casing of the fan motor, avoiding the wires/delicate bits obviously, and let rip. I gave it a minute or so working around the motor.
Then a set of Mole grips (Other inferior brands are available) on the shaft where the spring clip washer was, and start giving a bit o' wellie forward and back. I found that my Mechanic's Tourettes kicked in around this point.
Noted a little movement, so proceeded with the tug of war and swearing malarkey. Each shoogle was enough to move the thing a little more each time. A gentle wiggle on the fan blades at the same time for a little extra leverage, but not too much force as I was concerned about tearing the blade assembly off the shaft. Manufacturing quality suggested they were a 'dollop of blu-tac' fit.
Finally got a full 360 rotation of the blades, but they were stiffer than my grannies porridge. Pump in plenty of Penetrant fluid, I recommend the 3-in-1 stuff, some WD40, a splash of Kerosene, a soupson of red wine (accidental).
(I find it better when freeing-off things to make multiple, quick, back and forth actions, rather than constant 360 rotations.)
Once it was moving a lot more freely (about 10 mins or so) hooked it up to a battery and let it spin. Off she went, helpfully cleaning the bench area around my vice by dispatching the metal filings in a radius of about 5 metres. While it was spinning I kept a steady stream of WD40 into the shaft and armature areas of the motor. Then flushed it out with carb cleaner.
I hope this might give someone some hope if their fan motor is seized, and could potentially save forking out for a new one. Don't give up on it! That's not to say a different motor might well be terminal, but mine was about as stuck as one could imagine and it's now running like a champ!
I snipped the old destroyed captive fitings to use as washers, and fastened the fan assembly back on to the radiator with a proper nut and bolt, and a hearty helping of Coppaslip.
I shall wire a wee independent switch, as has been suggested elsewhere on here, to manually run the thing from time to time or during bouts of particularly, ahem, 'spirited' riding.
