Salvation ONLY in the Lutheran Church?

Not according to C.F.W. -

May god keep you from becoming entangled with this false teaching regarding the Church, namely, that the Lutheran Church is the true visible Church of Jesus Christ in the sense that you can be saved only in this church! The Lutheran Church is indeed the true visible Church, however, only in the sense that it has the pure, untainted truth. As soon as you add the qualification "the only church that saves" to the Lutheran Church, you detract from the doctrine of justification by grace through faith in Jesus Christ and mingle Law and Gospel. May God keep you from this error for the sake of your own soul and those who will be entrusted to your care.

C.F.W. Walther

Law and Gospel p. 385

32nd Evening Lecture, June 19, 1885