Last summer, I replaced the saggy rear leaf springs on my 65, mainly to bring the rear end back up to specs. Well, after replacing them, the passenger side spring would squeak, so I would spray them with silicone spray that worked for awhile, but the squeak came back. Well, when I was in a motorcycle shop getting some lube for my chain, I noticed some lube that had wax in it. I used the spray on my motorcycle chain that is available at just about any motorcycle shop. Anyhow, it worked great.
This stuff resists water and is o-ring safe so it won't hurt rubber bushings.
It outlasts anything else I've found so far, and I know several people that have started using it. Anyhow, I used it on my rear leaf springs of the Mustang and it hasn't squeaked since.

 

I need some for my bed

 

Very funny. Idiot.

 

What's the name of the stuff? You wouldn't be keeping it a secret, would you?