Update - another Hyundai dealer looked at the car, as per the recommendation from Hyundai Corporate. They took this much more seriously and kept it for 3 days, but I ended up in the same situation. Basically, they can't do ANYTHING unless they can reproduce the problem (which is too random for it to happen exactly when they are driving it.) So now it's going back to the original dealer's service team tomorrow for one final attempt at solving the problem. Then I guess back to Corporate.