hi...im ken and i have a 1958 johnson outboard (cd 15) its mounted on the back of my boat in the shop with a large tub of water to facilitate water circulation...im pretty shure there's enough water there to have water circulation but i dont...i dought the impellor has been replaced since 1958 . I presume impellor replacement would be the first thing to do however i havent dont a visual inspection yet...do i need any other parts to replace as long as im in that area of the motor...are there any problems inherent with these older motors that i should know about...please reply...thanks kenny J