Just about any kind of silicon sealant would probably work, the blue stuff in a tube (RTV?) is easy to use. Plus this kind of stuff would allow you to put those back on if you ever want to.

__________________
1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k