If you are in the Greater Phila area Bill Legall of "Miller Sound" in Lansdale, Pa. is a real craftman and can do just about anything with speakers. You can check out an article about him at 6 moons.
You can buy a speaker refoam kit from Ebay for about 20 bucks and do it yourself. There is even a guy on Ebay who will refoam the woofers for you if you ship them to him. They are easy to remove.
Get on Ebay and do a search on "advent woofers" and check it out.
Gordon Waters at Audio Atlanta has refoamed many Advents. I think he charges $30 per speaker plus return shipping. They're on the web. If you go to AudioKarma Gordon posts there a lot under GWaters. Audio Atlanta is also an advertiser there. It is dangerous to run the speakers with rotted surrounds. The coil will start slapping around in the gap and deform the former or worse, short out and possibly damage your amp.
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