  We study the transport equation describing a dense system of gluons, in the
small scattering angle approximation, taking into account medium-generated
effective masses of the gluons. We focus on the case of overpopulated systems
that are driven to Bose-Einstein condensation on their way to thermalization.
The presence of a mass modifies the dispersion relation of the gluon, as
compared to the massless case, but it is shown that this does not change
qualitatively the scaling behavior in the vicinity of the onset.
