When the OSW put together their Detroit to Buffalo mainline, 15 MLW RS-23s were purchased secondhand to handle online traffic (a pitifully tiny number of carloads at first, thanks to Conrail’s neglect of the CASO) as well as free up some of the RS-18s that were being used as overpowered switchers on the NStC&T’s lines.

These units were classified as DL10b, presumably for their similarities to the class DL10 roadswitcher.

All of them remain in service.