On 23 September 2006, 55 022 (D9000) "Royal Scots Grey" returned to the main line after a lengthy and extensive restoration at Barrow Hill, carried out on behalf of the owners by the DPS. It successfully hauled the SRPS 'Moray Mint' railtour from Edinburgh to Inverness, via Perth on the outward trip and back via Aberdeen. On its second working two weeks later, severe damage occurred to the number 2 end engine. The engine suffered from "a leg out of bed", a term which means the engine con-rod breaks out of the engine crankcase. This left "Royal Scots Grey" still able to operate but on one engine only. By January 2007, the faulty power unit was removed from 55 022, put into storage and replaced by an ex-marine Napier Deltic engine modified for rail use; work was completed by "Royal Scots Grey"'s restoration team in August 2007. After extensive testing at the East Lancs Railway the locomotive hauled its first tour since the previous engine malfunction on RTC's 'Autumn Highlander' with 50 049 and 40 145 in October 2007. 55 022 successfully hauled a number of charter tour services during 2008 but the replacement marine-sourced engine gave rise for concern following the discovery of oil in the coolant and at the end of August the locomotive was removed from future large railtour duties. The locomotive continued working mainline duty by visiting other preserved railway and moving other non-mainline registered locomotives.