I have a Mandarin Yellow Ahab that I bought soon after they became available. (That's got to be at least a few years ago.) The feed has been hacked and the nib has the EMF mod. This pen is in regular rotation and is often being cleaned and/or soaked.
I have had zero problems with staining or break-down of the barrel/section or the cap in any way.
However the clear piston has turned a slight yellowish/brown color over time, but it operates normally like when new. The yellowish tinge to the piston may be due to ink staining. I tend to use yellow or orangeish colored inks in this pen that shade a lot when the pen is flexed. Apache Sunset is a regular, but I've never seen Apache Sunset stain any other pen before. So I'm on the fence about blaming the ink.
I have several other Ahab and Konrad pens that were purchased either at the same time as the Mandarin Yellow Ahab or after. None of those pens is showing any signs of break-down or staining either. I'd say there are at least a half-dozen "Vegetal" Noodler's pens kicking around here - in addition to the Ebonite and Acrylic versions.
Conclusion: So-far nothing to worry about, and that doesn't look like it will change.