Caption: CN M-420 3501 (MLW 5-1973 #M6071-02) poses at the Sydney Shop in the dying days of CN service to Cape Breton in early September 1993.

In May 1973, the 2501 entered service as the world's first locomotive equipped with a Comfort Cab. CN worked with both Canadian locomotive builders beginning in the late 1960s to provide increased crash protection for crews as well as electric heating, improved insulation, armchair seats, a refrigerator and hotplate. After 1973, all newly built road units for CN would include a Comfort Cab. (See CNR Diesel Locomotives Vol 2, CNRHA 2014, for a detailed history of the Comfort Cab.) The MR-20a units also featured a freshly designed Zero Weight Transfer (ZWT-2) truck to reduce wheel slip. Finally, the order for thirty M-420s introduced the diagonal stripes to CN road freight locomotives.

CN displayed the 2501 for employees at Central Station in Montreal, while 2502 was on display in Sydney in early June 1973. Beginning in October 1986, CN began a 15-month program in Moncton to lighten the 2500 series units by restricting fuel and sand capacity. Upon returning to service, CN added 1000 added to their number, reflecting their assignment to secondary duties common to the dwindling number of ageing RS-18s. The unit was retired on Tuesday, November 25, 1997, and sold in 1998 by CN subsidiary CANAC to the St. Lawrence and Atlantic in Maine. It operated as their 3501 until the Hudson Bay Railway purchased it on Sunday, April 18, 2004. The Keewatin Railway running between Flin Flon and Lynn Lake, Manitoba purchased it in 2007 and assigned it the number 2400. It continues to operate, having borne the number 2402 since 2008.

In early October 1993, CN began to lease their trackage east of Truro. Railtex was the initial operator as the Cape Breton & Central Nova Scotia. Their choice of ex-CN R18s and, particularly, C-630Ms as motive power introduced a golden era between 1993 and 1997 that attracted railfans from around the globe. In late 2001, Sysco, a provincially owned steel mill closed in Sydney as did nearby coal mines owned by Devco, a federal Crown Corporation. The closures hugely impacted traffic on the CB&CNS. By Tuesday, December 30, 2014, Railtex successor Genesee & Wyoming closed operation of the Sydney Sub east of Tupper near Port Hawkesbury on Cape Breton Island's southern shore.