Has anyone done this? Can't seem to find a way to drop a rental in Koper and get to Trieste.
There are regular buses Mon-Sat: http://arriva.si/en/naslovna/aktualni-vozni-redi-ceniki/arriva-vozni-redi/mednarodni-promet/piran-izola-trst/
There also appears to be a daily bus service by Crnja Tours that runs on Sundays, too.
Thanks, Dejan for the quick reply and the link.