Just a thought, but is it possible that the diff is over-filled and some fluid blew out of the vent? I had just completed a 100mph+ "test run" down an empty stretch of highway when I noticed it. Come to think of it, the fluid that leaked looked brand new!

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"It's not about how fast you can go, but how well you can go fast."

Bob in Richmond

'97 S320 (LWB), Ruby Red Metallic, 73k miles
'97 S420V, Smoke Silver Metallic, 155k miles