phaser 7760 problem

When I've replaced developer my phaser 7760 has a problem. Coverage on cyan and magenta is poor (especially on center of the page), and on black or yellow is ok. Some friend told me to open it again, and pour some toner into developer housing. Other sad that maybe i have to replace cyan and magenta developer housing, but before I replaced developer, it printed just fine (had a problem only on one colour heavy coverage). I have printed only about 25000 pages. Is there any way to "force" it to use more toner (it seems that it's problem) any other way than onenig it again?

Thanks, and sorry for my bad english