  Let $R$ be a ring spectrum and $ E\to X$ an $R$-module bundle of rank $n$.
Our main result is to identify the homotopy type of the group-like monoid of
homotopy automorphisms of this bundle, $hAut^R(E)$. This will generalize the
result regarding $R$-line bundles previously proven by the authors. The main
application is the calculation of the homotopy type of $BGL_n(End ((L))$ where
$L \to X$ is any $R$-line bundle, and $End (L)$ is the ring spectrum of
endomorphisms. In the case when such a bundle is the fiberwise suspension
spectrum of a principal bundle over a manifold, $G \to P \to M$, this leads to
a description of the $K$-theory of the string topology spectrum in terms of the
mapping space from $M$ to $BGL (\Sigma^\infty (G_+))$.
