the 1980 Democratic Primaries in Puerto Rico, The First year that Primaries in PR were perscribed by law, the continuing contest between incumbent President Jimmy Carter and Challenger Ted Kennedy saw a decently close win for Carter.
The Nature of the race was one that very much resembled regular PR Races, with Carter being almost uniformly supported by PNP Dems (As he supported statehood) and Kennedy by PPD Dems (As the Kennedy's had a longstanding relationship with the PPD and support for the Estado Libre Associado).
It should also be noted that the PPD's founder, longtime President, and Former Governor Luis Muñoz Marín died around a month before the primaries, with grief sorrounding his death likely contributing towards Kennedy's defeat in the predominantly catholic Archipelago.
In terms of coalitions, Carter won thanks to his landslide margins in the San Juan Metro, with San Juan itself netting him around 2/3rds of his entire vote margin, by contrast, while Kennedy kept it close throughut the rest of the island, his strong margins in the west and south central/east of the island helped keep Carter's margin to 3.45%
Lastly, in 1988, the then PPD Senate President Miguel Hernandez Agosto, would later accuse Carlos Romero Barceló of asking Carter to close down a federal investigation into the Cerro Maravilla scandal, in exchange for winning Carter the presidential Primary in Puerto Rico, in a famous exchange where both men came across as Petulent children. (https://www.youtube.com/watch?v=U4385G-RU_4)