  We provide quantitative information in the form of a rate of metastability in
the sense of T. Tao and (under a metric regularity assumption) a rate of
convergence for an algorithm approximating zeros of differences of maximally
monotone operators due to A. Moudafi by using techniques from `proof mining', a
subdiscipline of mathematical logic. For the rate of convergence, we provide an
abstract and general result on the construction of rates of convergence for
quasi-Fej\'er monotone sequences with metric regularity assumptions,
generalizing previous results for Fej\'er monotone sequences due to U.
Kohlenbach, G. L\'opez-Acedo and A. Nicolae.
