Unfortunately the only solution I see is to vent, even when it's cold enough that you don't feel you need to. I guess Arc shell is relegated to non-arctic conditions. If the garment has Polartech insulation, it's called a "puffy," at least around these parts.Different Gore products have different levels of breatheability -- although none of them breathe all that well.As for venting, if I'm even close to sweating and I do vent. It's like the humidity was condensing into water instead of breathing out. Water vapor reaching shell condenses due to the cold rather than exit via the pores.As someone said--Goretex transmits vapor but not liquid water. MH shell seems to work better overall, never had any problems ever. ) for me there's no returning anything, everything I own is an extreme hookup of one kind or another.It has nothing to do with breathability or persperiation - you'll get this same problem with Neoshell and e Vent. Warm air coming out of your insulative layer is condensing on the cold shell.The fit of the looser shell causes it to be colder (air gap between it and the warm insulative layer).
This is one reason why I prefer insulated hardshells for very cold temperatures - you get the venting capabilities of a loose shell, but no condensation issues.
But with the new Arc shell if I'm working hard the inside of the shell actually gets dripping wet, along with the outside of the Compressor. If the previous shell was gore, but fit closer than the new shell, it would have a higher temperature differential between the inner and outer of the shell. I wasn't sweating detectably but the body still emits moisture and it's humid under the shell, so i gues that's the source. ) years under every imaginable condition and never had that happen that I recall. Well, it seems that there actually are phenomena outside the scope of your collective experience. Because 3/4 of the posters have no fucking idea what they're doing doesn't mean I don't. I saw you mention the venting and the temp and all the good details, if it's any consolation. Apparently I've hit upon a hitherto unknown combination or humidity, temperature, vapor pressure and thermodynamics that renders goretex useless.
This seems most pronounced when fairly cold, say teens and single digits (when it's warmer I usually vent). Ultimately gore does better the higher the temperature difference is, or the bigger the humidity difference is. For some combination of reasons the shell wasn't breathing out the vapor. I'm with the guy who said the difference is the fit.
(I'm a sweaty Viking; No e PTFE shell -- not even e Vent -- works for me if I'm exerting 30% unless I'm wearing e PTFE next-to-skin, and I layer over that if necessary for warmth.) I doubt that your Arc' Gore shell is defective. It's apparent that your new Gore shell has exceeds its breatheability limit when combined with a light puff for your personal rate of perspiration. Gore is less susceptible to contamination than e Vent but it's still possible that a tech-wash could clean away anything blocking the membrane that might have been picked up along the way.
(FWIW, I concur with those talking about loose fit.) So the answer is to either get rid of it or adapt to it. FWIW, if conditions don't necessitate full waterproof membrane then Polartec Power Shield Pro, regular Power Shield or even any of the many DWR coated windproof stretch wovens are a lot more comfortable.