I bought a 50MB (yes, megs) HD from an acquaintance. It was freaking slow connected to my Amiga, like 20-30KB per second. It also made a horrible high-pitched whine.
Figuring I had nothing to lose, I turned it over and squirted some 3-in-1 oil on the motor spindle. The whine started increasing in pitch as it quietened, and slowly the HD benchmark program started creeping up toward a more reasonable 1MB/s or so. I didn’t use that drive afterward, and just copied the, ahem, public domain apps and games off it and then threw it away.
I have not before or since sped up a computer by oiling it.