Personally - I would stay away from any greases. They have a tendancy to pick up sand and grit in the wind or from the ground and then would be carried into the recteptacle and start grind into the parts. If, they postions the grains in the right places,they could seperate the connections and start causeing a higher resistance. I would look into dry lubes way before a grease.
Something like the following - both are favorites (and WD-40)
Boeshield T-9 -<a href="http://www.amazon.com/gp/product/B001447PEK/ref=as_li_qf_sp_asin_tl?ie=UTF8&camp=1789&creative =9325&creativeASIN=B001447PEK&linkCode=as2&tag=aff iliatechie-20">Boeshield T 9 Rust & Corrosion Protection Waterproof Lubrication 12oz (aerosol)</a><img src="http://www.assoc-amazon.com/e/ir?t=affiliatechie-20&l=as2&o=1&a=B001447PEK" width="1" height="1" border="0" alt="" style="border:none !important; margin:0px !important;" />