D8020 was the third main line diesel acquired by the SRPS and was purchased in 1992 when British Rail put a large number of redundant Class 20 locos up for sale. It was bought from Toton, also with the aid of a grant from the Royal Scottish Museum, and had undergone some minor component recovery. It moved North to MC Metals for asbestos clearance and eventually arrived at Bo'ness in 1992. The missing parts were soon obtained from MC Metals and fitted and the loco returned to working order.

It saw regular use at Bo'ness, and was painted in a spurious livery of red, yellow and blue until failure of the seals on 2 cylinder liners in early 1994. The loco was then stripped down for overhaul. The engine had all the liners removed and resealed, and all the pistons and cylinder heads were overhauled. The auxiliary compartment and radiator fan room had all the machines and the radiator banks removed. These areas were then cleaned up, repainted and re-assembled. Some rewiring was done, and various sections of corroded leatherwork were replaced. Finally, it was repainted back into the original green livery carried, without yellow ends.

In the Summer of 1999, it traveled to Llangollen, and took part in their diesel weekend. For this, it received yellow ends to match Llangollen's own 20, D8142, and recreated an authentic late 60's pairing of weather beaten green 20's. The next outing was to Polmadie Open day in September 2000, before which it received a fresh coat of Green, with half-yellow ends and 66B shedplates.During 2001, it was agreed with the Strathspey Railway at Aviemore to hire the loco to them for 2 years. It moved North in September 2001 and has seen regular use, sharing duties with the lines own loco, Class 26 D5325. The loco has returned to Bo'ness and is currently in service. During May 2006, D8020 traveled south to Darlington for the centenary of the locomotive works where D8020 was built.

It was hired to the Wensleydale Railway between June 2010 and June 2011 and has now returned to Bo'ness.
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