No...Yanmar was indicating they were not very comfortable with a 15 degree installation. Hence the term "absolute maximum" installation angle. Of course, this wasn't the issue. The motor has been installed and functioning for over 20 years (two of which, the PO's owned it, PPO is dead). I can read a manual, and MY manual states: "The oil level (2.0 liters) should correspond to UPPER mark on the dipstick, with an installation angle of 7 degrees." Given the discrepancy with my dipstick, this begs the question; how much for a steeper installation? Which, Yanmar choose not to answer. They also completely ignored the discrepancy with the dipstick. Given that Yanmar acknowledge an extreme installation angle, I would have thought they would either make a suggestion or, say "we suggest you consult your local Yanmar dealer". NOT; If it worked for the previous owners, go with that! Thats really lame!
The place in NJ sees actual installations and gave me a straight forward opinion in response to the question I asked. I feel comfortable with that.
The reason I and others are concerned about disregarding the manufacturer's engine spec and adding an extra quart of oil is because doing so goes against a common understanding that overfilling an oil reserve can cause serious damage to the engine. But it sounds like you feel you got the best info from a reputable source, so I won't belabor that point. SailNet has lots of good amateur advice, but that only goes so far and in your case I would certainly defer to the experts.
You know what would be very helpful in a situation like this? Wouldn't it be great if we could get a highly knowledgeable Yanmar rep to come over and review a thread on SailNet, and offer up some solid advice from which everyone could benefit? Maybe someone from Mack Boring?
[P.S. As for the manual advice on oil level, I assume you are referring to the Yanmar "Operation Manual" ? My mention of variability on the dipstick readings was in reference to information contained in the Yanmar "Service
Manual". This is a different publication which is the manual used by service reps/techs. It's much more comprehensive than the basic "Operation Manual", full of exploded views and parts schedules, etc, including the transmission. Very handy to have if you own one of these Yanmars! But, like all the Yanmar manuals, it still has a few rough patches that result in seemingly conflicting info.]