It's been a while since I've jumped on UAL international but I used to jump frequently on them a few years ago. After the UAL/CAL mashup, they supposedly adopted some part of CAL's computer system (at least that's what was told to me). The ticket agents would tell you that they can't list you at the airport. They would say you have to list online. A couple times I could get them to list me but it was like getting an act of congress and a supervisor to get it done with a warning about having to list online next time. Other times I just went to DAL. All this happened at an international location. I don't remember jumpseating on them outbound at the time. Eventually I figured out what they wanted. They had created a way to list for the jumpseat on the ID90 website. You had to use the "commuting" option in the purpose of travel.

One thing about being at an international station, get there early to check in. At the locations I was at, they would keep all standby customers out at the ticket counter. They would tell you to come back at a given time (approx. 1 hour from departure). Then a few minutes after that show time, they start calling names and issuing tickets until they have cleared the standby list. Sometimes it gives you just enough time to hustle thru customs/immigration/security and to the gate. Not much time for duty-free shopping or eating. So bring a phone charger or something to do for the hour or so you're going to sit around by the ticket counter waiting for the show time.