You could try using ball catches in the runners of the traverser. Mount them to bear on ally (strip or angle) they'll act like gibs on a lathe slide?
Use the nice small brass/steel types though...... the plakkit ones aren't all that good for this.
As regards the wye point, if it worked oone way - why not the other? Is it slightly skewed offline of the entrance, or is there a fault in the frog/checkrails?
Emma
PS No mention in despatches for L/Cpl Izzy this time?