Our back in the day/redneck fix was to use toilet paper and white glue to reinforce small tears in cones. Laminate a few layers of tissue as you would with fiberglass. The stuff they sell for reconeing and dust caps is basically simple white glue.
It is best to dilute the white glue 50% with water.
This allows it to soak into the cone better-and weighs less.
Put the glue mix on the cone-place the tissue paper on it, and then apply a little more glue to tack down the edges.
I would disagree that "the stuff they sell for reconeing" is white glue. White glue does not stick to metal very well.
It is only good for porous surfaces.
The Dust cap glue does dry hard like white glue, but is stronger and not as thin.
But for a lower powered speaker like this it might work fine.