The story of Gus and his American BBQ is well-chronicled on the net among the expat community here in Korea. No need for SFP for regurgitate it here (when he can be out in the field eating at more good eats).
Take a read of this article: http://groovekorea.com/article/sweet-life-sweet-oak/
Sweet Oak is located 1 hour east of Seoul. There is an express bus that goes there every hour from Seoul. W10,000 one-way for a Premium First Class (super comfortable) bus seat. This is the option that SeoulFoodPatrol decided to go because we wanted to drink alcohol with our BBQ. Here is the conclusion. Sweet Oak is the Real Deal. It was awesome! Was it worth the bus drive? Yes. Would we do it again? Yes.
Naver Restaurant Info Link (Map, Hours, Links, etc).