Thanks Canuck, but the problem is moving thru the units, first the black went after the itb was replaced under warranty then the cyan , now a couple of months later the magenta next i expect the yellow.
This machine has only 12k on it now since installation at the beginning of the year, I need to do something to sort this out as its costing an arm and leg in drum units. I have two other variations on this model and so far i have had the same problem with one of them though they are heavier users and the wear is greater.
Mind you now i've looked at the faulty unit and the gears not exactly sure how to mod it as i havn't a workshop based machine to test it on?

There you go