A year and a half later, the fan began to hum like a cheap Chinese counterpart, which prompted me to disassemble it, clean it and lubricate it. Despite all the comments about the difficulty of disassembling it, I can say without too much modesty that in capable hands it is not difficult to disassemble it. But accuracy and care must be above all. At the electric motor, I lubricated two bearings. Used multipurpose gear lubricant. It's thick and should last a long time. After the maintenance, the fan began to work silently as after purchase.