Evolution of the helium abundance of a 41 M_⊙ primary in an initial 6 d orbital period massive binary under the case A evolutionary scenario described in Sect. 4.1, where mass loss and He-enrichment is driven by both stellar wind and binary induced mass transfer (solid red line). The dashed line represents our prediction of the evolution of Wd1-5 in a post-common envelope phase, whereby only stellar wind mass loss is present; for completeness the dotted line represents the continuation of the specific evolutionary model of Petrovic et al. (2005) if a common envelope had not formed. Finally, a brief episode of wind-driven reverse mass transfer during the pre-SN WC phase of the companion star accounts for the anomalous C-rich chemistry of Wd1-5.