THE FLT CREW RPRTD THE ENG LOST PWR WHEN THE HELICOPTER WAS AT APRX 100' WITH A FWD SPEED OF 50 KTS. WITNESSES OBSERVED FAINT GRAY/WHITE SMOKE EMANATING FROM THE VICINITY OF THE TAILPIPE SHORTLY AFTER LIFT OFF WHICH TRAILED & BECAME PROFUSEIMMEDIATELY BEFORE THE HELICOPTER BEGAN DSCNDG. SUBSEQUENTLY THE ACFT IMPACTED THE GND IN A LEVEL, RGT YAW ATTITUDE. THE RGT MAIN GEAR COLLAPSED & FOLDED UNDER THE BELLY, THE FUEL CELLS RUPTURED & THE TAIL CONE SEPARATED FROM THE CABIN. AN EXAM REVEALED THAT A MIXTURE OF FUEL & OIL HAD VENTED OVERBOARD THRU THE FLEXIBOX SEAL DRAIN LINE. ALTHO THE ACFT HAD RECENTLY BEEN WASHED, A HVY FUEL STAIN WAS NOTED ON THE UNDERSIDE OF THE HELICOPTER FROM THE GANG DRAIN TO THE FENESTRON. THERE WAS EVIDENCE THAT FUEL & OIL HAD LEAKED FROM THE JET HOLDER WHICH TRANSFERRED FUEL FROM A LINEAR LINE TO A ROTATING LINE. HOWEVER, AN EXAM OF THE FUEL (FLEXIBOX) & OIL (SEALOL) SEALS SHOWED NO IRREGULARITIES. THE CONDITION COULD NOT BE DUPLICATED DURING BENCH TESTING.