I don't think there is a 'best'. Even Vaseline will probably work just fine. All you need to do is put something between the dissimilar metals (AL and steel), which, left on their own, with a bit of moisture, develop an unholy relationship.
I've experienced it. I wish to do my part in preventing it.
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*Recipient of the 2006 Time Magazine "Person Of The Year" Award*
Commence to jigglin’ huh?!?!
"But hey, always love to hear from opinionated amateurs." -says some guy to Mr. Marshall.