All fans, even those big ones at home, need some maintenance
Just a drop of 3 in one oil
or machine oil
with no detergents in the oil, works wonders for any fan. Detergents in the oil pit the metal bearings because the 'detergent'is actually microscopic metal pieces that will scour the softer bearing.
Takes just a few minutes to clean and lubricate and much less work than going to the Marine
store, and back, disconnecting the old one, wiring
it up again with connectors or whatever and screwing it back on.
Instead; do this: At your leisure, unscrew the fan, any brand, from where it's mounted. While it's hanging by the wires, pull the blades straight out and off. Now, put a couple of drops of 3 in one oil or non-detergent motor
or machine oil, even axle grease works well, on the front spindle, axle, or shaft right where it comes out of the motor
and giggle it in and out and spin it a little and wipe off excess.
For the rear bearing at the shaft, tilt the fan facing down and slide a thin piece of wire through the rear vents and touch the place where the same spinner shaft exits the motor inside the fan enclosure. Now; the difficult part is to steady the fan while the thin wire is touching the shaft and slide a few drops of oil down the wire and onto the rear shaft.
If you cannot line things up, don't leave it dry now that you are almost finished, just tilt the fan at any angle where you could drop some oil onto the shaft by gravity. It will get messy but at least lubed up. Try not to drown the internals with oil. Oil does not conduct well, or may short things out or even attack the rubber insulation
depending on lubricant used.
If the internal wires or the switch are somewhat in your way, gently move then aside. Even if you must cut part of the case at the rear vents, it will not show and will make it easier next time. Wiggle the shaft some more, spray some WD40 or electronic cleaner onto the switch and exercise it, clean up the fan and re-fasten in place. Fan will be good for another 200 hours or more!! Then ....repeat next time; fans will last you for many years.