Cause of this particular problem was that the printhead cleaning module wasn’t moving out of the way (receding into the printer), and was fouling on the printhead.
Many repair shops won’t even attempt to repair inkjet printers because the cost of repair could easily out-weight the cost of a new printer, but I thought I’d at least give it a go (and if I wasn’t successful then I wouldn’t charge the customer)
First thing to try was to wash the printhead cleaning module, as it had a LOT of dried ink on and around it. This freed-up the movement slightly and you could push the cleaning module with your fingertips, but it wasn’t being moved by the printer. Something else is wrong…
The two cogs are driven by coil springs which are wrapped around the axle, allowing some degree of slip (like a clutch) when things go wrong. We can see that one ONE of the springs, the tang which engages with the gear wheel has been broken off
Printer reassembled and tested, £20 charged which included collection and delivery just a 5-minute walk away from me