white dots at magenta\ c452

hi friends
when i print solid magenta , i saw white dots.
when change magenta image Unit completely, for many days is true, but after about 2000 pages, my problem come back
tested with original toner/ diffrent paper / diffrent ticks , it's same

please help me

 

If the drum and imaging unit have been completely serviced, it could be a transfer issue. Transfer voltage that is. Which would be an electrical or power supply issue. I can't say i've ever seen marks quite like that though. They usually look like little crows feet.