  We use QCD sum rules to determine the difference between moments of the
non-singlet structure functions. This combination decouples from the singular
behaviour of the structure functions near x=1 as calculated in the quark-gluon
basis and thus should lead to improved sum rule predictions. However, we find
there are still very large errors due to higher order corrections. In order to
refine the error analysis, we study the effect of renormalon ambiguities on our
QCD sum rules results.
