Bizhub C451| Problem with printing gradation

[polyprint]

The Greeting all!
I have machine konica minolta bizhub C451. Month earlier problem was got with printing gradation. The Lower side of the sheet not completely to print.
I can not exactly express this on english. Put the photo.
Problem there is on CIAN, MAGENTA, YELLOW.
I do: clear lazer - no result, hard stop-(problem transfer belt or PH unit).
Any thoughts?

The Problem under red line.

[polyprint]

the light band.

[mo0651]

how old are drum (IU) units? rechipped? Looks like same prob on top side of paper.

[polyprint]

how old are drum (IU) units? rechipped? Looks like same prob on top side of paper. With many thanks for message.
IU counter =85 000 А4, not rechiped. Today change developer in CIAN IN ( developer from C6500 original)=gadation it was got better. Later do magenta and yellow.

[polyprint]

Clean PH unit(mirror, lens) not result.