SAN JUAN, Puerto Rico -- Going to the doctor in Puerto Rico has for years often meant getting in line. Now, it might mean getting on a plane. A medical exodus is taking place in the Caribbean territory as doctors and nurses flee for the U.S. mainland, seeking higher salaries and better reimbursement from insurers. Many of their patients, frustrated by long waits and a scarcity of specialists, are finding they have no choice but to follow them off the island. Among them is Marilu Flores, a 60-year-old rural mail carrier who is battling advanced rheumatoid arthritis.