As to the two rubber pieces, when I put the two side by side, these are the things I noticed: The CAT one is a little bigger and fills up the hole where the damper goes, the SS one is just slightly smaller than the hole. The CAT one has an inside lip too - I don't know if it really has any effect. It is hard to tell if the CAT damper is of firmer rubber or not. It feels harder, but there is more rubber there. The top of the CAT rubber is flat, the top of the SS rubber is rounded.
This is what Rick says about his: it is made by the very same manufacturer that made to original damper (i.e., OEM) using the same formula for the rubber, and that the damper is very common to many cars of the same and later era. He understands that the CAT rubber is firmer because when it was designed, the example was an older damper that had already hardened with time.
That's all I know.
Jay
Jay S. Laifman Pircher, Nichols & Meeks 1999 Avenue of the Stars Los Angeles, California 90067 (310) 201-8915