Stack sealant failure

See the attached pic. The sealant fell off partially exposing the opening where the stack vents into the chimney. I also see a white cotton(asbestos ???) material between the stack and the wall of the chimney.
My questions are:
Should I duct tape this exposed area as a temporary fix until I get a sealant to cover it up? I also have metal (aluminum) tape.
What is the sealant material I should use for a long term fix?

Thanks for any tips.

That looks like a product called Kaowool (non-asbestos). No need to tape it. You could go to your heating company and if they have any dry chimney sealer they would probably gibe you a small amount. About two cups would do it. Of not buy some vent pipe sealer at the hardware store. You could use the same stuff they use on wood stoves.

tk03........... thanks a lot for the info. I wasn't sure about the material to use.