CV axle keeps pulling out of driver side. Retainer clip not working? Need help.

I recently replaced the driver side CV axle on my '88 ST162 3sge GTS liftback. The old axle had failed because of torn boots and what not. I replaced the axle with a factory spec brand new from Oreilly. I checked all the measurements of the two shafts and they are identical but the new shaft keeps pulling out of the transmission every time I drive the car. I believe the retainer clip isn't engaging. Any help with this issue.

Old axle = no problems. New axle= pulls out. Dimensions of the two= same.

What am I missing here.