Thanks for all the ideas guys!
Sorry for the delay in getting back, too mant Xmas functions ..
History - about the 4th owner from new, now just done 100000kms as I said. Prev owner seems to have had it fairly well serviced & looks reasonable from previous experience (6th BMW, 5th K). Did the usual check arounds when I bought it apart from the swingarm & the high-torque pivots, put that off until recently when I had some spare time...
FD bearing looks good, no play. Been there done all that with the R1100GS before this bike...
Spline - no visible wear when I was in there for the lube (part of the whole remove the swingarm & do the clutch weep hole, was due anyway. Sort of discounted the driveline mostly anyway as clunk occurs with clutch out too, & hopefully not too much rotational inertia at 5kms or less coasting to a stop. Could always be wrong though.
Exhaust hanger - yep, noticed that & fresh oring on recently (after removing whole shebang & new never-seeze on all the bolts...). No effect on the clunk tho.
Stand: both up and away as per ready to ride; haven't tried recreating the noise with the bike on-stand. Had sort of discounted this as there seems to be plently of clearance to moving parts and the springs seem to be doing a good job of keeping both stands in the stowed position as far as I can see? (Did check torques on the main stand carrier while I was doing the swingarm anyway - never want them to have any excuse to be loose the loads they put on the gearbox main casting!)
Swingarm: Hmmmm ... got a spare one here (after hearing the horror stories of seized pivot threads & needing sabre saws to get things out!) and lower bushing looked cylindrical & un-worn/deformed... ditto for the torque arm ones on the FD and gearbox. Only one I haven't eyeballed is the upper shock mount, tho it is to toque specs.
Caliper: Will check the pads & pins/walls for wear again; I do have the 2 types of caliper mounting bolt as well (one shouldered, one not & they are to torque although I can't 100% recollect if the leading bold is the shouldered one or not (should be from the realoem diagrams) - something to check. No visible damage to the FD mounting lugs or the caliper, threads are fine & original.
Did just think of the brake disk itself moving, but the conical screws looked in & tight when I had the FD off...
Checked rear subframe, ABS unit & battery shouldn't be able to move.
HR69996: If you can duplicate that's homework I'll take you up on! <grin> ... this has been a niggle for me for a while, a bike with a frame as substantial as the one on the K12 shouldn't go 'clunk'! (Just like the white smoke on my original K100RT...)
Again, thanks for all the help - much appreciated here.