SILICONE ALTERNATIVE. For all those who do not like silicone, try a polyuethane elastomeric sealant, like the Sikaflex range. Superior adhesive range between different materials. When cured virtually indestructible. Can be used in aggressive enviroments, so an I/C engine room no problem. Potable so no contamination of water. Can be used under water. Can be sanded, though idon't recommend. I prefer to use some spittle from the hand as a final smoothing agent before curing. Can be overpainted with any paint system. Downside, it's expensive, but you will not be buying by the box only a tube. From any good builders merchant or Amazon.
Keith

You will also find that Silicone sealant, IF used in a constantly "wet" area will also fail and looses its bond. Please only use this stuff sparingly and only use where it only gets damp or the odd bit of water splash. Some people use it to seal prop tubes to hulls, Highly risky in my opinion and wil, in the end fail and you will end up having to refit the prop tube all over again. My motto, "if you gonna do it, do it right, but first time!"