A damaged bearing is evidence, not just a replaceable part. Surface marks, discolouration, wear location and debris can show whether the root cause was lubrication, contamination, load, installation or electrical current.
Lubrication and contamination
Too little lubricant allows damaging contact; too much can raise temperature through churning. Wrong viscosity, incompatible grease or degraded oil also shortens life. Fine hard particles indent raceways and create repeating stress as rolling elements pass over them.
Fit and alignment
Loose fits can creep and fret, while excessive interference reduces internal clearance. Shaft and housing shoulders must support the rings squarely. Misalignment, bent shafts and soft foundations create uneven load zones that a new bearing will not correct.
Preserve the evidence
Record operating conditions before disassembly. Photograph the bearing, seals and lubricant, mark ring positions and inspect mating surfaces. Trend vibration and temperature so the corrective action can be checked after restart.