Help please. I have a Johnson outboard with no data plate. No model/serial number info. The rear of the cowl shows the seahorse imblem, and the number 18. It is a twin cylinder. Is there any other place's on the engine where I might find some usable number's to ID this motor. It run's great, but is in need of a replacement prop soon. If I can not ID the motor exactly, will I still be able to replace the prop? Thanks. Darrel.