See here:
"When sleeve bearings fail, one of three things typically happens. Almost all failures will occur because of issues with the lubrication.
Failure one, worn bearing- This occurs when the lubrication is insufficient or the rotating component too unbalanced,. The rod begins to wear away the sleeve material to a point when the cylindrical space is no longer round. The rod will begin to vibrate producing an audible noise as it rotates. In instances such as this there is nothing that can be done, but to replace the bearing or more typically the entire fan.
Failure two, reduced fan speed - A situation can sometimes develop where the lubricant partially evaporates, or becomes more viscous then its operational tolerances will allow. It then resists the magnetic forces rotating the fan blades causing the entire assembly to rotate at a lower then normal RPM. The results of this type of soft failure can be serious if the fan is cooling an essential device like a power supply or CPU.
Failure three - Complete failure. Occurs when there is an absence of lubricant, or when highly viscous lubricant overcomes the rotational force from the fans' motor. In these cases the fan will not rotate at all, and devices which need cooling may overheat. This is one of the more common failures among power supply fans because of the continual amount of dust they suck in and their elevated operating temperatures. This type of failure can also occur when improper lubricants are used which become highly viscous through age or as a reaction to operational temperatures."
Taken from
http://www.frostytech.com/articleview.cfm?articleid=193&page=2
Notice this statement : "Failure one, worn bearing- This occurs when the lubrication is insufficient or the rotating component too unbalanced,. The rod begins to wear away the sleeve material to a point when the cylindrical space is no longer round. The rod will begin to vibrate producing an audible noise as it rotates. In instances such as this there is nothing that can be done, but to replace the bearing or more typically the entire fan."
When you re-oil a sleeve fan (since the other types are not easily re-oiled), you only fix the lack of lubrication. The vibration, wear are not repaired, which leads to uneven loading and accelerated wear. As was said above "nothing that can be done".
Lots of people re-oil their fans, I included. But with the acceptance that the fan life is nearly over, and this is nothing more than a stop gap.
AND I DID READ YOUR COMMENT: "To poke at him he must be one of those middle class types that are overpaid and act that they are or have to be professional in everything. " -Very "unprofessional" of you.