I print artwork (cards) on 250gm xerox silk paper. I'm getting faint streaks developing down the A4 print, starting on the left side, if I print more than 5 copies at a time, if I set to print 20

Try this link:

https://www.support.xerox.com/support/phaser-6110/support/enus.html

Streak in only one color:
Check the condition of the print cartridge, and replace as necessary.
Verify that the print cartridges (C/M/Y/K) are genuine Xerox cartridges,
and replace if necessary.
http://download.support.xerox.com/pub/docs/6180MFP/userdocs/any-os/en/user_guide_en.pdf

either the drum developer or fuser if you can show me a sample I can tell you which it is

Watch the development stations to see if there are white lines that match. The stations are easily removed from the left side. If so, stir vigorously the station and manually turn the developing roller

I believe what you are referring to is the drum inside the toner cartridge. The drums are usually very strong colors, blue or green and if it is streaking then the drum cleaning blade has failed on the inside and you need to replace the cartridge.

Replace the toner, try rocking it 1st but be careful of spills.

Here are "little" specification:

Body installation method desktop page printer
Photosensitive medium OPC drum
Exposure method semiconductor laser
Development method Toner projection development
Transfer method by roller
Separation method by curvature
Cassette pickup method by pad
Multifeeder pickup method by pad
Drum cleaning method by blade
Fixing method on-demand
Delivery method face-down/face-up
Toner supply type by toner cartridge
about 6000 prints (A4, single-sided; at 5% image ratio)
Warm-up time in standby: 0 sec (at power-on: 10 sec or less)
Print area top: 5 mm; bottom: 5 mm; left/right: 5 mm (if envelope, top, bottom, left,
right: 10 mm)
Printing resolution 600dpi
First print time 9 sec or less (approx.; A4)
Print speed (A4) 21 pages/min (approx.)
Cassette paper size A4, B5, A5, Legal, Letter, Executive
Multi-purpose paper size A4, B5, A5, Legal, Letter, Executive, Envelope DL, Envelope COM10,
Envelope C5, Envelope Monarch, Index Card, Custom Paper Size (width
76.2 to 215.9 mm, length 127.0 to 355.6 mm)
Cassette paper type plain paper (64 to 90 g/m2), heavy paper (91 to 120 g/m2), recycled
Multi-purpose paper type plain paper (64 to 90 g/m2), heavy paper (91 to 163 g/m2), recycled
paper, transparency, label paper, envelop (DL, COM10, C5, Monarch,
B5)
Cassette capacity 250 sheets (approx.; plain paper, 64 g/m2)
Multi-purpose capacity 1 sheet
Delivery tray stack 65sheets (Face-down) /1sheet(Face-up Output Slot)
Memory 8 MB (internal; no optional memory available)
Operating environment
(Temperature range) 10 to 32.5 deg C
Operating environment
(Humidity range) 20% to 80% RH
Noise 52.8 dB or less (during printing; based on ISO9296; announced noise
emission)
Power supply rating AC100V±10% (50/60Hz ±2Hz)
Power consumption (Maximum) 790W or less (approx.; 20 deg C; for input of rated power supply;
including peak value lasting 1 sec or more)
Dimensions 370 (W) x 375 (D) x 258 (H)mm
Weight printer: Approx;11kg; toner cartridge: Approx,0.8kg(2.5K)
Option paper feeder

One of two things.
If the streak is a line. No visible print in the streak, Then most likely the drun cleaning blade is bad and the drum unit will have to be replaced.
If the streaks are sort of reprint. a faint reprint of what is already on the page, then you need to replace the fuser.

Your yellow problem sounds like a bad yellow developer housing. Take the drum out and look at the developer housing, You will need a flash light to do so. See if the roller is solid yellow. Even if it is there may not be any developer left in the housing.
The Cyan sounds like the drum since it gets worse as it prints.
That can also be caused by the transfer belt cleaner. But that normally is the opposite. It has a rainbow sort of streak and it gets better as the machine runs.