Whatever the issue, I am actually submitting an RMA on the card. After running with the stock fan for a bit, it started to fail again.
It could be unrelated, so we'll have to see. It's a good thing I didn't sell the stock fan!
THe good thing is, I actually had a X800XT lying around.
I'm in the process of selling pulled parts from someone else's gaming system. I had to put the VM-101 so it sticks of it pretty far to avoid the XP-90, but it actually runs really well with the fanless solution!
In that case, it looks like the card either A) was defective to start with, but got worse over time or B) really did suffer heat damage.