Mystery colour streaks - Will pay for solution

Hi, I am desparate and willing to pay anyone that can help solve my printer problem for me.

S3D support and Craftunique are unable to isolate despite much problem solving.

PROBLEM:
Random and slightly diagonal lines/streaks across my PLA prints.
1.5yr old Craftbot3 (CoreXY design) with moderate usage.
Problem only started recently.
Started on head1 then eventually started on head2.
Layers are about 1-2seconds long

SOLUTIONS TRIED:
Rails - lubricated
Material - swapped with fresh reel
Speed - various
Extrusion - layers all look uniform and accurately laid, only colouring seems affected
Temp - not enough time for temperature to fluctuate so consistently within or between layers
Something loose - layers all look uniform and accurately laid
Stl file or slicer - printed previously without issue

It is only a problem with these parts, because they form part of a desklamp and have light shining through them.

Thanks :)

Attachment 14001

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rotate the part on the slicer bed and reslice it and see if the lines change directions Post the STL file we can understand what the part is. What infill rate are you using or is this just a couple perimeters? Lines always in at the same layer height?

well to me they look like layer start/end lines.
What is your layer start set at ?

Unless i need a particular area very smooth, I always set my start and end points to 'random' .

Sorry for my late reply,
Thanks for answering
I'm sorry but the file has ip restrictions on it, i cannot send it out.
I've been printing these parts with any problem before.
it only started recently.
It is just a 3 perimeters.
Streaks are always at random heights and locations
I think it is heat related.
It is only a problem with thin parts like this.

@curious aardvark
all the start/end lines are stacked at the back of the part, so it doesn't cause marks on the smooth curved front side

you could try replacing the heating element/cartridge, they're fairly cheap and pretty straightforward to change on most machines.

Have you upgraded simplify 3d to 4.1 ?
And if so when ?

I had no end of issues with 4.1 and am now back to using 4.0 it's just better.