It was now 15 or 16 years since the start of production of Sentinel and Vanguard locomotives, and major overhaul or complete refurbishment was required on many of the early machines. Capital expenditure was being restricted by many companies but particularly by the British Steel Corporation and the National Coal Board, so the marketing department concentrated on these customers offering a complete service for refurbishing to "as new" standards. This business proved very lucrative and extended the life of Sentinel and Vanguard locomotives ensuring a continuing demand for the spares.