This whole situation is making me think that in my case, it's time to move on from the ST. My dealer is going to cover the 2nd diff under a parts warranty, but it's looking like it's an every 30-40k mile "wear part". The 1st diff was put in last March.
I have an appointment tomorrow afternoon, and should have more info, and if they are still on back order. If it's a month wait again, this will be 3.5 months out of 30 months of total ownership that it's been at the dealer. 10k cam phasers requiring a new long block, 30k the 1st diff, 69k the second diff. I bought this thing thinking that it would have been vet'd pretty well since it's basically a police interceptor. I guess I was wrong. Being in the quality field, I didn't make a big deal about the first issues, but when the diff went a second time at roughly the same interval that's telling me this isn't an isolated failure especially since the failure mode is identical.