Richard,
My advice here would be to abandon extensions on Peco point motors because many of the motors in my practical experience have so much sloppy movement in the armature (armature shaft is a sloppy loose fit in the coils) that it is possible for the armature to move side to side without the tip of the extension moving at all, consequently, a turnout doesn't change because the extension doesn't move. I raised this with Peco who claimed they'd never had this problem before in 30+ years, but most (if not all) my Peco motors are like this. I directly attach my motors to turnouts. If you really need extensions, I would strongly recommend Seep point motors as they are far better made and certainly here in Sydney, are actually cheaper than Peco and have a much more reliable switch built in.
Graham Plowman