Heat rigging needle, poke a hole on top of the head, fill it with whatever, heat needle again and "paste" the lures own plastic to fill the hole again. Never had a leak.
I seal my redfins with some of that hot melt glue u use to put on rod tips..light it with a lighter and let it drip..works good and u can remove it to reload them pretty easily is u have to..shud work for bombers too.