Hi mjb - To be absolutely honest I was a collector before I built a layout, so at the moment all of my M/N's are still in their boxes - I have twenty four. However, one similar loco that I do run is the Hornby West Country Crewkerne, and the front bogie has started to derail when passing over points - it's on the layout all the time, but does not move to often. I use Code 75 track which may be the problem. The Hornby Bulleid Pacifics have been around since 2000 - they were described as "super detail" which they were at the time, but I'm not sure if the earlier ones had a deeper profile on the wheels which allows them to "ride-up" at the smallest iregularity in the track. Sorry not to be of much help. BB