An interesting alternative for Duct seal in Europe (France - Belgium) is a product called FILGUM from a company called GEB. it is pretty resistant on metal frame. Does not come off easily. I did some tests on older speaker frames.
Alternative is an epoxy compound but more messy to work with and does not stays "rubbery".
Alternative is an epoxy compound but more messy to work with and does not stays "rubbery".