Just about three days ago, I broke a blade off of an Intel CPU
cooler's fan. I puzzled about what to do, as the fan is an unusual
type and I don't have any other Pentium III compatible coolers sitting
around. What I finally did was to super glue the blade back on. The
repair appears to be robust after two days worth of running. What's
more, the balance appears not to have been affected at all by this
little "whoopsy".

Good fix. I was in a similar trouble but didn't have the blade so I
placed two small rubber belts held on the nearest blades to balance
the fan, worked quite well.

I've had limited success oiling fans, usually it won't last long as
the oil appears to evaporate or go somewhere else. I tried several
oils for motors and none of them last. Some evaporate and some harden
and end up locking the fan. I belive the manufacturer used some sort
of special grease, I have seen similar grease used in sleeve bearing
motors for video heads in Philips VCRs that after years of operation
preserves its properties intact.