Thanks KLAUS. My wife actually found the link you provided in your post last week ... and I finally looked at that bellows more closely this afternoon (it's black, not grey on our car), and had (what first appeared to be) a beige "rubber band" at the base of the accordion bellows, toward the firewall. This 'rubber band' is actually made of a thin foam (~1/8 inch thick, ~1/4 inch wide), and literally fell off when I wiggled the bellow. I'm not sure of its function, but the base of the black accordion bellows actually has several pre-stamped holes in it (!), apparently to allow air to flow in (these holes are hard to see unless you really crawl under there, and look for them!). My guess is that the foam seal just keeps crud from going in there, and maybe (?) limits loss of vacuum in the 'system'. Any other thoughts? After removing the remnants of that foam seal, the hissing (per my wife) has gone away ... but we'll see how long that lasts ...:)

BR

Bernie