While packing for my move, I found some original rubber stack rubbers. The bottoms near the air filter were hardened and distorted somewhat relative to the remaining circumference. It is not nearly as bad as what was pictured above.
I suspect the atomized fuel leaches the plasticizers out of the rubber aking them hard. But, before losing the plasticizer solvents, the gasoline additives bolster the solvents and initially make the rubber even softer. Then the airflow/differential pressure distorts them, and they harden in that position as the solvents get sucked away.
We don't know if the replacement rubber compound is the same as that made in the Honda supplied units. Perhaps it is more sensitive to today's gasoline formulation.
But, clearly the distorted rubber bits are not ideal. And replacement is likely in the path to recovery. But, rubber and plastic sometimes respond favorably with heat.
I would (and probably will after my move) make a round form/ collar from hardware store pipe for the distorted parts, and use a heat gun to see if the part can be reformed. If so, the "when cooled" hardness ought to work in your favor to prevent distortion in the future.
I think it's worth a try.
