I added a tire/tube sealant to my tubes. I have had good luck with this sealant preventing flats on 4X4 trucks. I was suprised at the flimsy plastic nut holding the tube centered in the rim. When I added the sealant I put a regular nut on to prevent the stem from going into the rim. What is the groups experience with sealants and have others changed the flimsy stem nut?