hi, i have a nylon prop which i want to change to brass,i can not get the prop to unscrew, i think it was put on with some sort of locktight, there is no lock nuts, the prop screws onto shaft,i dont want to damage old prop, as i am might not get a brass prop with the same thread as it is a old model no longer made, the name of the motor launch is neptune, a billings kit launched in 1958,i dont know when they stopped making this kit