We have a Jeanneau
DS40 that has a yanmar 54hp and love the engine. Love having the power we have and a couple of times really really glad we had it. The arm chair guys will tell you 40 is good but get into a tight pinch and find you do not have enough power is not the time to figure out you should have gotten the bigger engine.
As for Yanmar we have more than once had a someone on board to do a bit of maintenance
and I said Yanmar and they smiled and said great engine and will take a beating and keep on ticking -- and lasts a long time --
as for parts
we have not had a real issue getting parts almost anywhere we have been .
this may cause a bit of controversy but Yanmar probably makes the best marine
engine there is.