Tony,
Like Harold, I have a large number of PL13's fixed to Hornby point motors over the last 5 years with no problems with switching.
However, I did not glue the PL13 to the motor. I thought it may give me alignment issues. What I use is the ties that the Wife gets with her freezer bags. I rap one each end of the switch around the motor housing. This secures the switch, however leaves enough slack so that the switch does not affect the motor and enables easy dismantling if required.
Hope it helps
Rick