It depends on what kind of powerloss. It could several different things. But to most common would be the stator. You said that they never opened the engine to check any componats in it. Mostlikly thats what it is. Thats the problem im having with mine. To fix it your looking about 5 to 7 hundred dollars, but the good thing is if you can do it yourself it will hardly cost anything, all you will paying for is labor anyways.