Incorrect installation of the seal (in reverse) on the driven axle.
Installation of the seal with unsuitable tools (without the Fersa mounting tools).
Mounting of the bearing without using Fersa mounting tools.
Mounting the bearing without mounting the inner side O-ring.
Bushing installed without the shaft O-ring. Failing to replace the cap and O-ring with new ones
Bearing installed with excessive torque (no axial clearance)
Premature failure in bearings.
Lack of grease in the bearing
Oil contamination in the differential.
What to do to increase the lifespan of the bearing