CMYK spots on print

No, that's not what it means.
If printer heads are not aligned, CMYK colors (Cyan, Magenta, Yellow and blacK - the usual colours in a printer) will not print in the correct place.
Assume a dark grey dot is to be printed. For this C, M and Y colored dots have to be placed exactly on the same spot. But if heads are not aligned, the three color dots will not be exactly in the same place. Therefore you will see Cyan, magenta and Yellow dots adjacent to each other instead of one dark grey dot.
It is always a good idea to align the print heads every time a new cartridge is installed.

It means that the printer has calculated that you have made the maximum number of prints that the manufacturer has calculated that the drum can effectively do before the prints shows signs of spotting or fuzziness. Strictly, the drum cartridge should be changed, but if the print image is still good and the printer still works, leave it in. The printer drum cartridge will be rather pricey, somewhere between $50-$100, depending on model.

change the drum of your cartridge

How do I clean white or black spots on printed documents? Description: First make 10 to 15 copies of a blank, white sheet of paper.
If you still see the spots on printed documents after making multiple copies, clean the drum unit as follows:

1. Remove the drum unit and toner cartridge assembly, and then remove the toner cartridge from the drum unit.
   
2. Position the print sample in front of the drum unit so you will know the exact position on the drum that is causing the poor print.
   

3. Turn the black gear on the drum as you check the surface of the OPC drum.
   The OPC drum is photosensitive so do not touch it with your fingers.
   

4. When you find the substance on the drum surface that matches the print sample, gently dab the surface of the OPC drum with a cotton swab that is lightly dampened with isopropyl alcohol.
   
Note
• Do not use a scrubbing or wiping motion because this might damage the drum.
  
• Do not try to clean the surface of the OPC drum with a sharp object, such as a ball-point pen, because this might cause permanent damage to the drum unit.
5. If the print quality still has not improved you need to install a new drum.
   

Create a mask or layer for each spot color you want to print using only black. When printing spot colors anything on the mask in black will be printed in the spot color. For foils, print a couple of layers of black ink before you print the foil to get a very good effect. Remember to check the overlay option so the paper doesn't get ejected.

can be solves by changing whole drum unit because problem with bias grid (black strip on chager)

You either have a bad spot on the drum or a bad spot on the fuser rollers. Replace the cartridge first. If spot continues, take cartridge out and get inside with a flashlight. You'll probably find a piece of paper stuck to a roller.

each dots comes .5mm gape in one by one at different places pls check and replace a new drum.

There are several causes of those.
So go to Xerox.com
Click "support and drives"
then in the product name box, Type DC12
Then any line click support
IN the search box type "spots" and read the relevant solution.

Clean carona on drum. blue slidy tab, sounds like you are using non brother toner is that correct? Replace with OEM, Can also be worn drum