any Ca-based grease of the lighter variety (NLGI 1 or 0) would do the trick. Ca-greases are very waterresistant and usually contain corrosion inhibitors, the Ca-soap itself also has anticorrosion properties. Ca-greases are extensively used for the lubrication of ships machinery on deck and protect the equipment from corrosion, even in a salt water environment. The max operating temperature is around 60 degrees C which would not pose a problem in this case. The biggest problem would be to get it in a small quantity, but a local lubricants reseller should be able to help you out.