^spyder, while yours is a horror story without a tragic ending as you were able to stop the car without further incident, you did possibly miss out on having your diff vent checked initially (there have been at least two procedures identified related to the vents) it does appear that whether the oil leaked out the vent or the seal is immaterial, the oil disappeared and your rearend locked up solid while you were driving. One has to assume that repair or replacement was covered by the warranty. But it would also appear that due to time when this happened your car does not have the newest fix so would presumable be included in the February recall. You can take it in now to be inspected but if you insist on an immediate fix if problems are identified you may not get the most current up to date fix. That's the reason for waiting until Feb., as the complete procedure and/or parts have yet to be exactly identified.
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When more than one friend wants to ride shotgun

No, I
do not work for GM,
but if I did, the G8 ST would not be DOA!