Pennsoil sythetic blend mixed 50:1 works great. Or you can run the johnson oil or whatever brank you choose. Impeller???? Everything that needs to be done to the engine for the oil injection disable has been done. Pretty simple to do on a johnson. The VRO is part of the fuel pump. Simply unpluggin it kills the VRO, then the pump still works as normal. Then the oil tank should have been removed and a plug put on the VRO chamber or it can be removed and a plate installed. Either will work. You may look into replacing the water pump impeller as a prevenative maintenace.