ACCORDING TO THE PLT, HE EXTENDED THE GEAR, GOT A SAFE GEAR DOWN INDICATION & MADE AN APPROACH WITH THE FLAPS RETRACTED. THE GEAR WARNING WAS NOT HEARD. THE PLT STATED THAT AFTER THE ACFT ROLLED ABOUT 1500 FT AFTER TOUCHDOWN, AND WITH ALL 3 GEAR ON THE SURFACE, THE RIGHT WING WAS SEEN & FELT TO DROP UNTIL THE RIGHT PROPELLER CONTACTED THE RWY. A MECHANIC (FBO EMPLOYEE) OBSERVED THE ACFT LAND & NOTED THE APPROACH WAS STABLE, THE LANDING GEAR WAS DOWN & THE FLAPS WERE UP. HOWEVER, HE STATED THAT AFTER TOUCHING DOWN, THE ACFT STARTED TO ROLL OUT, THEN 'HOPPED A LITTLE, LIKE HE PULLED BACK.' THE MECHANIC SAID THE 'DOORS CLOSED, LOOKED LIKE GEAR WENT UP & LOCKED, WENT DOWN & SLID ON ITS BELLY.' AN FAA INSPECTOR FOUND THE GEAR HANDLE DOWN, THE FLAPS UP & OBSERVED NO CIRCUIT BREAKERS WERE POPPED. DAMAGE WAS FOUND IN THE LANDING GEAR EXTENSION/RETRACTION SYS, BUT NO PREIMPACT FAILURE WAS FOUND.