Dennis,
You can try Steve’s Shop. Although they are Yanmar mechanics, they know their way around an A4. They are in Charlestown but are very hard to get this time of year.
There is one other mechanic that I’m familiar with in the harbor but I wouldn’t recommend him unless you are desperate...good luck!
Another thought— any neighbors that may be able to assist? Constitution is huge as you know and perhaps someone would be able to take a look for you??