Corroded Bolts - What's the best preventative?

[Phalcon51]

Greetings All,

In the process of replacing the water pump on my '86 300E I've found several bolts with corrosion heavy enough to make it difficult to extract the bolt (the 10mm belt tensioner through-bolt and the long 8mm bolt that goes through the upper part of the "Y" bracket in front of the tensioner). I'm replacing the bolts and cleaning out the holes as best I can, but I'd like to know anyone's opinion on what to use to prevent further problems of this sort. I was thinking of either using waterproof wheel bearing grease (the type used on boat trailers) or anitsieze (the silver-grey type). Which would be better, given the environment, or what other suggestions might you have?

Thanks,

Gary