Hi, I have trawled the web and am so confused.....I have a Yamaha outboard motor serial number 40HMO 6H4 S 184080 The only thing that I have determined is that it is a 40HP short shaft. Can anyone help me to identify what year this engine was made. I know it is old, it runs well but I would like to identify it's age so that I can try and find a Maintenance Manual for it. Any help appreciated, thanks 