Can you flame treat the PP surface for better adhesion by hot melt? 3M makes DP8005 and DP8010 acrylic low surface energy adhesives but expensive. Hot melts to bond PP require high temperatures and adhesive film as 2-sided PSA may work better.
The plastic inner housing is cracking/chipping away from ball bearing vibration most likely. You will see bearings coming loose, or popping out, which will crack the outter metal housing. Danaher Motion makes an all metal inner/outer housing for likely 50% more cost. The inner metal housing...