Ran out some old stuff I got from the LBS years ago. Can't remember the brand, the label wore off.

Anyways, i needed someting in a pinch, so I dug around the garage, and grabbed the 90W differential gear oil. Wait a second, it sayd "GEAR OIL"....hmmmm wonder if this will work. After all, it stays in the differential for years with gears grinding away, why not a bicycle chain?

Instant silence... now that is impressive. Even better, and smoother than the old stuff I was using. I just clean the chain every couple rides with WD-40, then squirt on some Diff oil from the squirt can. Takes only a couple minutes.