Yanmar is a bit of a pain when it comes to who their dealers/distributors can sell to....if you're not in the area they can't sell to you.
I've been able to locate a couple of head assemblies in the US, so if needed I'm okay there...assuming "my" dealer can find them.
Started taking the heat exchanger off and found this:
Can someone remind of why this happens? I remember it being mentioned in a thread but I didn't find anything in a search.