Because it was thrashed. The 1951 IRRS journal shows that SLNC engines took an absolute hammering from operating over such an undulating and curved PW, not to mention other issues such as water. Immense strain was put on loco underpinnings and the gradients meant that boiler water could be surging all over the place - the gauge glasses were not always comforting to look at ! A careful examination of SLNC photos towards the end shows that the locos, once sparkling clean, were filthy - even on the ceremonial ‘last train’. IE there was little spare capacity available to do anything more than maintain the basics as the line ran down. Between 1951 and 1957 the three ‘large tanks’ all went to Dundalk for overhaul, leaving the 2 Loughs in almost constant use. The UTA doesn’t seem to have done much to them - they don’t even seem to have been cleaned before being put into use. 27 was beautifully painted up in the late 60s as seen here but I don’t think much mechanical work was done. The SLNC’s best loco at the end (which worked the very last steam empty stock positioning run in Oct 1957)was apparently ‘Enniskillen’ which was overhauled in 56 - although you wouldn’t think it from her external state at the end. 27 pics from David Cooke on Flickr.