I don't see why any TOC would winningly f*ck up their stock and crew diagramming, seat reservations etc willingly. GC are trying to find the best way around the issue of low class 180 availability and the use of SSOs at Doncaster allow them to use one less unit with (hopefully) minimal disruption to passengers. As for the argument that they will want to start sell tickets because this is "regular" that is b*llocks. They could'nt sell tickets Sunderland - Doncaster due to the fact that it is not scheduled to call at DON, as the term SPECIAL stop order suggests. Furthermore, it's not as if the fitters and senior management are sitting down weeks in advance saying "Right, we think there'll be lots of passengers going to Doncaster on X date, lets make sure 180xxx fails on Crofton then, I know, we can sell loads of GC Only SUN-DON tickets, we could even put in the mechanical difficulties on the website 2 weeks in advance to let everyone know...." Not quite like that is it?! With regards to crewing it's a nightmare as well as disruption to 1N29's timings along the whole route, GC are doing this to offer the highest possible level of service on BOTH routes regardless of 180 faults , this is the solution.