Step back and look at the system that broken equipment is part of.
Focusing your attention on a specific piece of equipment is essential to repairing that equipment. But then you need to step back and look at the system the equipment is part of.
For example, a large air intake blower motor sounds like it threw a bearing, and it's barely turning. After you remove the motor, you grab the rotor and can barely turn it. You hear a faint grinding sound. This motor's toast, but is replacing it all there is to this repair?
Let's say the mechanics find the blade is balanced. You find the motor is properly mounted, there are no bonding deficiencies, and your power analyzer shows fairly clean power. You really can't find anything wrong. And you know, there have been no errors in lubrication practices. What could be wrong?
Go outside and closely inspect the intake grill. Does this adequately protect the fan blades from being hit by water? If not, you may have found why this repair won't last long.