Only time I took retracts apart was when the servo lead was partially severed by the case joint. Whoever in factory assembled the retract had allowed the lead to get jammed between case halves. Of course the retract already installed in the model - it was never noticed till after a few flights - the bumps and grinds led to the case biting through the lead.
I fixed it and that retract still works to this day years later.
My question though now is ... 5mm pin ? That's quite a pin for a Viper ? I assume we are talking about the Viper EDF Jet ? Its not a big heavy model - so I am wondering why 5mm pins ? I assume the old retracts had 4mm pins ?