Question on chimney chase top repair

I'm in Southern New Jersey. My gas chimney is leaking water when it rains and the first repair company I had look at it said the seal on the chase top (the big plate that covers the chimney with a hole in it for the center pipe) (See
http://chimneykeepers.com/images/chase_top1.jpg for a picture) had some gaps in the seal and is getting rusty.
He caulked it for now and said he thinks I can get a few more years out of it if they "wirebrush complete chase top then seal it with silicone, paint with aluminum/fiberglass flashing sealer". That's $200. He guessed a new stainless steel chase top would be $700-$800.
I don't know anything about aluminum/fiberglass flashing sealer but it sounds more like a caulk than a paint. ???
My question is: Is his job worth doing and will it really hold for a few more years?
(Yes, I know I should go for the new SS replacement but that's not my question.)
Thanks,
Ted
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I would think that elastomeric roof sealant would be a better product. http://www.henry.com/Cool_Roof_Coatings.28.0.html look at Aluminum emulsion and elastomeric acrylic .
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