CQ Mpc7501 itb unit dropping toner

Hiya. I have this problem I would love to solve. The image transfer unit builds up toner on the lip by the mylair by the cleaning brush. I have swapped the ITB unit completely, renewed devs, drum units and fully vaced out several times but give the machine 1500 copies there is a little ridge of toner appears on the mylair and ridge mainly in the middle and I just can't fatham it out.

Just had it again dropping speckles of toner and vaced again, checked the brush is turning and the orga is turning to get rid of the waste toner and all is fine there.

Any help or if anyone has had anything similar that would be great.


Thanks loads

tim.