I have a 1963 40 H.P. Johnson Electromatic that I have been having shifting problems with. I bought a manual for it and it said one of the causes could be not using the proper lower unit oil. It called for type C. What is type C? What's the differance in it and regular lower unit fluid. I have not found it in local stores but I have not been to a boat dealer yet. Is this an oil that is hard to come by and if so does anybody know where I can get some?