Most of the work I do myself, both on my wife's 300e and my 400e.
I have used an indi shop in Durham twice for emergency work. I believe the name is B & K Motorwerks. EXCELLENT people. High quality work and fair prices. They are off of Roxboro and Hwy 147 in downtown Durham.
Do a search under "Good MB Shops" and there are a few recommendations for a shop in Raleigh. I may try them next time I need some major work.
Congrats on your new 400e.