First, if the nuts are stripped that fasten it to the tub, they'll need to be replaced. Turn off the power and remove the heating element. Check the seals where the element goes through the tub. If they look worn or cracked, take them down to your local home center and match them up. Clean the two holes in the tub good with rubbing alcohol. Replace the element seals and nuts. You shouldn't need any sealant. If you want to use a sealant, after cleaning it with alcohol take a fine grit piece of sandpaper and rough the bottom surface only (under the tub) use 100% silicone on the bottom only. Give it 24 hours to dry.