If you have the 3YM20, I have the same engine. Had it put in brand new 8 years ago. You are right about the tranny oil. 30W. The question about transmission selection while sailing is one that has been debated ad nauseum. Never, however, sail with it in the forward position. I always sail with it in reverse to keep the prop from spinning. I come to a complete stop before I shift into reverse after shutting down and a complete stop before I start up again and shift to forward . The problem occurs when staring up, again. Sometimes the shifter won't allow you to go back to neutral. Don't force it. I just start with it in reverse and then shift to forward. Yanmar came out with that directive a few years ago. I asked the mechanic who installed the engine and several other mechanics about that. They all seemed to agree that it probably came out as a CMA response from Yanmar because of, maybe, a suit against them for a faulty transmisson. Most likely someone forcing the tranny into neutral from reverse. None of them reported seeing any damage from sailing with it in reverse. Of course, these people make a living servicing engines and trannys. I have over 500 hours on mine and not a bit of trouble. I'm sure others will chime in, also. Check the archives here and other sites about this. Get a cooler full of your favorite beverage because you are going to be at your computer for a long time and may come out with no more info then you went in with.
