On June 22, 1995, about 1212 eastern daylight time, a Piper PA-31-350, N530JB, registered to Key Largo Air Service, Inc., made a gear up landing at Opa-Locka Airport, Opa-Locka, Florida, while on a 14 CFR Part 135 nonscheduled, international, passenger flight, from Great Harbour, Bahamas, to Miami, Florida. Visual meteorological conditions prevailed at the time and a visual flight rules flight plan was filed. The aircraft received substantial damage and the commercial-rated pilot and six passengers were not injured. The flight originated from Great Harbour, on June 22, 1995, about 1010. The pilot stated the flight was scheduled to land at Kendall-Tamiami Executive Airport. While on approach to the airport he noticed the landing gear handle was in the up position and not the neutral position when he attempted lower the landing gear. The gear handle was hard to move and when he forced it to the down position nothing happened. He diverted to Opa-Locka Airport. When all attempts to extend the landing failed, he landed gear up. Maintenance personnel stated that to extend the landing gear after the gear up landing they raised the aircraft. They serviced the hydraulic reservoir and used the manual extension pump, which operated normally. Postaccident examination of the aircraft by NTSB personnel showed the right main landing gear door line was ruptured, which resulted in loss of all hydraulic fluid. After changing the door line the landing gear system operated normally. The failed right main gear-up line had a manufacturer date of 1979. The aircraft was manufactured in 1979. Piper Aircraft Corporation annual and 100-hour maintenance inspection report requires that all fuselage fluid lines should be checked for leaks at each inspection. Additionally the lines should be pressure tested after each 10 years and each 5 years there after. Aircraft logbook records show no record of the failed line being pressure tested in 1994. See attached inspection report.