Brother 9130cw prints fade to blank

[cscce]

This MFC 9130cw is the first Brother color laser I've had to work on. Sometimes it prints fine but MOST of the time the image will get fade out until it's blank (see samples). The service manual lists several possible causes for blank or uneven density problems, including the main pcb and the LED pcb, but I wanted to find out if this series is prone to any particular component failure. All supplies are OEM. Only 5,400 pages have been printed on this machine but it's out of warranty. All drums, belt & fuser have 65% or higher life remaining and toner cartridges are almost full. Stopping the printer in the middle of a cycle shows no toner on the belt, but the belt has a charge on it.

Here are 4 sample pages, the first one shows how the page should look, the last one is almost blank. The right side of each image is the leading edge.
20161024160425018_0001.jpg20161024160425018_0002.jpg20161024160425018_0003.jpg20161024160425018_0004.jpg
Thanks in advance.

[Elmtech]

Mark the devs and drum to see if they rotate, UI have had issues with dev engagement clutch but this usually causes an error. Also there have been problems with the HVPS contacts so you can reseat the HVPS.

[theengel]

Also, check for moisture in the paper.

[cscce]

Mark the devs and drum to see if they rotate, UI have had issues with dev engagement clutch but this usually causes an error. Also there have been problems with the HVPS contacts so you can reseat the HVPS.

Thanks for your suggestions. They pointed me in the right direction. The clutch seemed to be fine and I found that printing in B&W was always perfect so I thought maybe there was too much drag when printing in color. I checked all of the drums. The yellow drum was significantly harder to turn than the other drums. A dab of Superlube seems to have fixed the problem. The boss didn't want to buy a new set of drums.