Thanks to everybody who has responded so far. This is all just sort of confirming or at least extending my thought process on the "problem." For 20+ years, I pretty much counted on getting 3-4 seasons of 75-100 days of paddling out of my gaskets, barring some stupid rip from a stick or catching a sharp screw head when shouldering a boat (put a huge rip in a neck gasket that way).
Maybe the gaskets were better 'back in the day' and the ArmorAll wasn't doing any better at protecting them, etc, or maybe the 303 just reacts differently with latex even though it provides better UV protection. Whatever the deal is, it's disheartening to have gaskets lasting 1/4 to 1/2 as long as they used to last, when you would think they'd be coming up with better ways to make them last longer. I'm definitely gonna try the silicone spray and/or the McNett SealSaver. I've just had enough of what 303 seems to do to the gaskets overall, and I'm boycotting it for at least the next two seasons.
If nothing else, at least ArmorAll is super cheap in comparison.
So many rivers, so little time..........