Any thoughts and any words of wisdom, most appreciated.
Our c7000 is intermittently throwing a c2243 code...

Background. Machine c7000 2010, 11Million, well maintained, all OEM parts and consumables and regularly serviced before and during our ownership.
Situation. Cyan was clearly showing faint lines in the image due to a lack of tonor, investigation showed that the blue dev unit was the cause with inconsistent toner coverage across its roller.
Seeing the dev unit was at 99% life I installed a new cyan dev unit, dev, drum and charger (in accord with the field service manual)
Ran all the adjustments in the required order and ran first job no worries.
Having completed this job it entered adjustment mode as normal and codded out with c2243.

I know this is linked to the cyan motor M16
So repeated [initial drum rotation] and machine ran next job, only to code out again afterwards.
So checked motor in I/O all four speeds - certainly motor has not failed, nor gears, appears to be running fine.
So checked sensors PS85/6 and these also come up ok.
In case I had got a dodgy drum I swapped new drum unit for the original one - ran initial drum, auto color adj, auto gamma, fine.
Ran next job and coded out within a few hundred sheets.

Any thoughts?
I know the manual also suggests PRCB and the DC power supply/2, I'll assume the latter is fine as it's not coding out on the other drums.

Thanks in advance