There are 9 pads in total, 3 in the right hand section (these will be worst), 3 large ones in the centre and 3 more at the left.

All the pads should be lifted out, washed out thoughly in warm water and then dried. A nice sunny day helps!

The photo shows all the pads clean and reinstalled.

Whilst the printer mechanism is out, is also worth checking and cleaning the pipes that feed ink from the ink pads to the base of the unit.