On April 4, 2000, about 1724 eastern daylight time, a Dassault Falcon DA-20, N175GA, registered to Grand Aire Express, Inc., operating as a Title 14 CFR Part 91 positioning flight, experienced a failure of the left main landing gear to extend for landing and an excursion off the runway edge during landing rollout at Opa Locka, Florida. Visual meteorological conditions prevailed and an IFR flight plan was filed. The airplane sustained minor damage and the ATP-rated pilot and commercially-rated copilot were not injured. The flight left Louisville, Kentucky, about 2 hours 30 minutes before the accident. According to the pilot, during the approach to Opa Locka's runway 27R, when the landing gear handle was selected down by the copilot, none of the three landing gears extended. The pilot commanded gear handle up and back down a second time, but again, to no avail. At that point, the pilot executed a go- around, and on his downwind leg, he commanded the reading and execution of, "Procedure A" of the checklist for, "Landing Gear Extension Failure". At the completion of the "Procedure A", the right main and nose gear indicated extended; however, the left main gear indicated not extended, and the pilot lost hydraulic boost to the flight controls while simultaneously observing both hydraulic quantity indications decreasing. The pilot declared an emergency and stated he would be landing as soon as possible. Reference to the "Operating Handbook, Abnormal and Emergency" that was on board N175GA and used by the crew during the failure of the landing gear to extend revealed that there is a "Procedure B" and a "Procedure C" to be executed, in sequence as necessary, to insure extension of all three landing gear prior to landing. The aircraft sustained superficial under-wing skin scraping of the left wing. A puncture in the left wing leading edge droop resulted from collision with a runway stanchion, but no structural member was damaged. Speed tape was applied to the wing droop perforation by a company mechanic, a ferry permit was issued by the FAA, and the airplane was flown to the airline's headquarters in Louisville. According to the airline's Director of Maintenance, the failed component was the attaching hardware for the hydraulic emergency slide valve, P/N A2-23769, mounted to the left main landing gear door-actuating cylinder. The emergency slide valve's function is to allow continued hydraulic operation of the landing gear door with the operable hydraulic system in the event of a single hydraulic system failure. The emergency slide valve is common to both of the aircraft's hydraulic systems; therefore, a leak caused by failure of the mounting hardware results in a double hydraulic system failure. On April 26, 1984, the product support division of Dassault Falcon Jet promulgated Service Bulletin FJF 32-160 recommending that the attachment hardware for the emergency slide valve to be increased in size, (4-mm bolt diameter to 5-mm). The compliance wording states, "when the component is returned for major overhaul or repair, or upon request." Maintenance records revealed that the incident aircraft had not had the SB complied with. A copy of SB FJF 32-160 is included as an attachment to this report. The left MLG door actuator, PN A23729-0, SN 095, was examined for failure analysis at a repair station/subsidiary of Dassault Falcon Jet Corporation with NTSB oversight. The attached data plate revealed a pre-modification part number and measurement of the emergency slide valve attachment bolt diameters confirmed that SB FJF 32-160 had not been complied with. Both bolt shanks revealed minor cadmium plating decay and stress corrosion. Both bolt shanks revealed fatigue failure and total fracture at the location where the first thread, (closest to the bolt head) was machined. The repair station engineering report is an attachment to this report. The FAA Data Section of Aviation Flight Standards, AFS-620, researched their database for Falcon 20 landing gear door actuator service difficulty reports from 1974 to the present and found no other cases of hydraulic failures due to emergency slide valve attachment hardware failure.