My initial thought is that a recall won't count for lemonade. This is a voluntary action by GM. One part of the letter says "Dealer will replace pinion seal" but elsewhere calls for inspection first. Until the dealer and customer letters come out it would remain somewhat unclear if each and every vehicle in the timeframe will get a new seal, and if any that have already been replaced have yet to have the newest seal, and therefore might get done all over again.
Think of it in this light, if this fix is truly a permanent fix then it is a fiax and not a failure to correct. Only failures to correct would stack up for lemon law. For example your state says three failed attempts at repair and you have already had two selas replaced, even one time including a complete diff, this third seal fixes teh problem and it never raises its ugly head again; voila, no lemon.
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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!