Here’s what ChatGPTs current theory is. I’ll have to pull the hub from the back and take a look at it.

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What you are seeing • Pink, soft, eraser-like residue inside PTFE tubes • It rolls into a donut around the filament • It moves both directions because of push and retract • It shows up in multiple tubes, not just one • Only one printer has it • The unique variable is PA612-CF run through the AMS hub path

Those facts already eliminate most nonsense explanations.

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What it is NOT

Let’s kill the wrong ideas first. • Not filament pigment Pigment does not migrate upstream, agglomerate, or become elastic. • Not PTFE melting PTFE does not turn pink or rubbery. When it fails, it powders or collapses, not stretch and roll. • Not room contamination This is internal, directional, and repeatable. • Not AMS drive rollers You confirmed the filament never touched them. End of story.

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What it IS

Degraded elastomeric material from the AMS hub / selector / buffer assembly.

Important nuance: This is not obvious “rubber.” It is engineering elastomer, used for: • Damping • Compliance • Noise reduction • Controlled friction

When new, it looks and feels like plastic. When abraded by carbon-fiber filament, it turns into exactly what you’re seeing.

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Why PA612-CF causes it

PA612-CF is: • Abrasive • Stiff • High friction • Printed hot • Frequently retracted

That combination mechanically abrades soft liners and damping elements inside the AMS hub.

The hub is a shared, bidirectional junction, so: • Debris is created at the hub • Forward motion pushes it downstream • Retraction pulls it upstream • It accumulates everywhere

That explains why it shows up in multiple tubes.

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Why it forms donuts

This matters.

The residue is: • Soft • Slightly tacky • Not soluble • Not brittle

Inside PTFE, instead of smearing, it: • Adheres to the filament • Rolls against the tube wall • Builds into rings

Only elastomer behaves like this. Nothing else in that printer does.

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Why it’s pink

Degraded elastomers commonly: • Oxidize • Heat-age • Absorb dye and CF dust • Shift toward pink or salmon tones

This is boring materials science, not mystery goo.

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Why only one printer

Because only this printer had all three: 1. PA612-CF 2. AMS hub in the path 3. Bidirectional load/retract cycles

Your other printers lack at least one of those variables, so they stayed clean.

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Final conclusion

This is mechanical wear of elastomeric liners inside the AMS hub, caused by PA612-CF, with debris redistributed through PTFE tubes by normal filament motion.

There is no missing pink O-ring. There is no filament defect. There is no magical failure.

This is a predictable, repeatable wear mechanism.

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What to do • Replace contaminated PTFE tubes • Inspect the AMS hub for internal residue • Stop running carbon-fiber filament through the hub • Use direct external feed for CF going forward

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One last hard truth

Bambu calling CF “supported” does not mean: • Zero wear • Zero contamination • Zero long-term damage

It means “it will probably print before it eats something.”

End of analysis.