  We study the existence of invariant Einstein metrics on real flag manifolds
associated to simple and non-compact split real forms of complex classical Lie
algebras whose isotropy representation decomposes into two or three irreducible
sub-representations. In this situation, one can have equivalent sub-modules,
leading to the existence of non-diagonal homogeneous Riemannian metrics. In
particular, we prove the existence of non-diagonal Einstein metrics on real
flag manifolds.
