Heat oven to 275-300 deg. Score meat's skin with a sharp knife, making a cross-hatch pattern. Pulse garlic, onion, oregano, cumin, chili, salt and pepper together in a food processor. Add oil in a drizzle and scraping down sides as necessary, until mixture is a thick paste. Blend in the vinegar.
Rub this mixture well into pork, getting it into every nook and cranny. Put pork in a roasting pan and film bottom with water.
Roast pork turning and basting every hour and adding more water as necessary, until internal temp = 195 deg and meat is very tender. Raise heat at end of cooking if necessary for browned and crisp exterior.
6.4lb roast - 3hr@275, 2hr@300, 30min@375 worked well with tender meat and crisp exterior; 4lb roast - may be done in 3hr@300
Let meat rest 10-15min before cutting it up. Serve with lime slices.