Success:
5/30 LH415 IAD-MUC. I booked that one on 5/25 through the call center after seeing availability on united.com

FAIL:
5/31 LH572 FRA-JNB. Call center said they couldn't see availability, even though I could see it on united.com. Then I tried to make a booking on the web site but the process failed after I clicked the "Reserve" button.