Do you know about this website?
http://timeshare.pueblobonito.com.mx
You can log in with your resort, contract number, and last name.
I own at PB Emerald Bay and when I log in at this site, I click on the FAQ link on the right of the page. There, I can see a heading of, "Depositing with RCI / Club Pueblo" and email addresses of people to contact for reservations under that. The FAQ is a little out of date, but you could check on the Sunset Beach FAQ to see what it says.
Geekgirl