2400 miles is a lot- but I wouldn’t give up on it yet. It sounds like wind resistance is the chief complaint, probably caused by old calendaring. Calendaring is when they run a fabric over a hot roller which fuses the fibers. This gives that side of the fabric a ‘shiny’ look.
The old 0.8 Downproof from pre-Momentum days was heavily calendared on both sides to increase the downproofness; it was so shiny that apparel made from it made you look like a spaceman. Eventually stuffing and unstuffing shells made from the 0.8 flexes that calendaring enough that its wind resistance is impacted. That’s probably what’s going on with your Aero too.
Try using a spray or wash-in water repellence product like McNett’s Reviv-X or similar.
I think the Montane gear was the best of the shell gear, but their brand has been hard to come by since they parted ways with their US Distributor. I’m not familiar enough with the current crop of commercial shell gear to make a meaningful recommendation for a potential replacement.
