The clutch lever pull felt fine, but it was incredibly difficult to click the shifter between gears. I just am not used to checking the clutch freeplay on a regular basis so this didn't occur to me.
There was maybe an extra 3mm of play at the lever compared to the factory specification, so it didn't take much stretch in the clutch cable for this to happen.
Anyway, I have been rather paranoid about running T6 5W40 on this bike in the summer months because it tends to run VERY hot. Before I knew the clutch freeplay was the culprit, I assumed that the oil had sheared down too much and was to blame.
I have T4 15W40 in there now and a brand new clutch cable on the way.