Welcome to the SBO Forum. It can be difficult to find a mechanic that you feel comfortable using.
Hope the suggestion turns out to be positive. I found my best source for difficult engine tasks can be found servicing the diesels for the commercial fishing vessels. Owning a boat most of the service tasks, I find, become the work of the owner. Due to cost savings and safety of resolving issues when the boat is out on the water. In port when the challenge is out of my wheel house then asking at a chandler store or on the commercial docks has been fruitful.
My most recent contact came from a store I frequent. I rationalized, they have more to loose giving me the name of a bad mechanic than a good mechanic.