bizhub C351 problem with yellow IU

[printech]

I've got this C351 that started to fade on yellow when he IU was at only half it's life, replaced the yellow IU and the prints were OK for a while (abou 10k copies) then the same thing happened. When trying to print a yellow test page (in tech mode) at 255 density, it starts pretty well on the page and then fades out . I checked the toner supply, the gears turn OK, there is no blockage ( I don't think the problem is with the toner supply motor because there is one motor for both yellow and magenta hoppers). I weighed the IU's and the yellow is abut 250 grams lighter than the others , like there is not enough developer or toner in it. The average toner coverage for yellow is about 6% , replaced the toner cartridge as well (KM toner) but no result. It seems that the problem resides in either the developer or toner supply. Any ideas about this issue?

[minimerlin]

Have you checked the one way gears of the toner supply system, the motor turns one way for magenta and the other way for yellow. I have had problems with Image units not doing correct life, also have had trouble with the transfer belt pressure rollers. Is the fade in the feed direction or front to rear?

[printech]

The fade is in front to rear direction. The way I checked the gears was by manually turning them both ways. Minimerlin, do you have the part number for that gear you're talking about? Thanks!