ghost said:You should be able to enter and exit Argentina on your US passport. Some rules have changed. You will not have to pay the $131USD entry fee when returning because they waive that for Argentine nationals carrying a US passport. As they do regarding "overstay fees".
Two weeks ago a friend was in a similar situation with an expired AR passport , so she simply used the US passport for entry and exit. No problems.
That's great news. I've just arrived in Colonia - at the Buquebus terminal I asked the immigration officials if I could leave with my DNI and enter Uruguay with my US passport. They could not think of a reason to say no, so I did that. In a month I'll re-enter Arg. with the passport, so I'll be technically there and will be able to travel with that passport as I've always done.
I asked about overstay fines. It is Arg. 300, regardless of the length of the overstay.