How do I lubricate a noisy fan?

You should really replace the fan. The ball bearing has probably seized and adding lubrication will only help for a few days. As a temporary lubricant you could use about anything with low friction.

I'd try 3 in one oil. WD-40 is mostly a solvent, 3 in one should give you a longer term solution.

Aerosol Teflon is another option.