An update on this in case it helps others:
We opened a claim with Subaru of America and they covered 25% of the repair cost. Not great, but better than nothing. Apparently there is no guarantee of help up to 125,000 miles.
Some things that might have affected their decision (though they said they didn't have a "big effect"):
1. The vehicle has been maintained by independent shops b/c a dealership was too far away (over an hour), including this repair. They "suggested" I take it to a dealership for this issue, but then the dealership would tack on $100 to inspect the problem prior to any decision about reimbursement (i.e., the dealership would not take my independent shop's word for it). I wasn't willing to risk adding insult to injury.
2. The vehicle was fixed after 100,000 miles, although I had documentation for the problem as early as 96,500.
3. I don't imagine Subaru coolant conditioner was used in coolant replacements after factory (twice if I recall correctly, at 60,000 and then during the timing belt work at 90,000). They never asked about this, however.