Recently had a disturbing loss of power on my 2007 Legacy with 211k while driving on the highway about 70mph. The power loss was accompanied by a poof of white smoke and haven't gotten power back yet. Now drives fine on flat plane but can hardly make it up hills. From what I've read so far it seems to be an omissions issue and not the head gasket which is a relief. Hoping for the right answer here. Heading in today to change valve cover gasket and front oxygen sensor, which had already been scheduled. No Subaru dealership nearby so my mechanic might need some input.