Try BALISTOL, this eucalyptus based oil invented in 1904 for the German army is terrific for virtually everything. It works very well for preserving and cleaning the Leica's vulcanite.
I use it for the upkeep of my camera's (Leica M5, Linhof & Hasselblad), the dashboard of my Volvo, the chain of my bicycle, the little wounds on my hands, the leather of my camera case and shoes and, last but not least, to protect me against the sun and cold hands.
See www.balistol.co.uk (I do not know the U.S. address).
It is good for gear, man and animal.