Water and Grease................
Dont use the grease, 3in1 oil or similar, not WD40, will be ok for the shafts, if oil dont work on the rudder then use the Graphite spray, but first try to find the cause of the binding, possibly, you have tightened the rudder horns to close to the rudder posts, just lift them a little to see if it loosens them
Mark
Etherow Model Boat Club