Can I use fantastic elastic glue for a rubber foam replacement?

Not an expert on speaker repairs but there are some considerations to be aware of. Genuine woofers (not the typical 6" car door speakers) like yours move the cone several millimeters for bass sounds. This means the cone must move freely from whatever suspends the outer ring. Special cone support like foam seals are usually designed to allow maximum up/down movement of the cone. Using any off the shelf seal may alter bass sounds, permanently damaging great bass. Perhaps writing to the manufacturer or search online may reveal the correct flex sealer to restore your woofer back to sound operation.