I agree 100% - Yanmar engines are among the best small engines available today.
However, Yanmar manuals
are some of the worst. (Stated only as 'my humble opinion' of course.) Many of the newer Yanmar motors (as well as other makes/models) don't have zincs. Our YHM30 (2005 model) doesn't have them. The word 'zinc' doesn't even appear in our manual. In hindsight, that should have been a clue.
Our Yanmar was a replacement for an aged Westerbeke
and we've learned lots of other little tid-bits along the way. For example, the fuel
system on our engine
is self-bleeding. The manual made no mention of this either.