What was found
MAIN DOOR: UNABLE TO OPEN MAIN CABIN DOOR FROM INSIDE USING NORMAL METHOD. AFTER FLIGHT/ SHUTDOWN (VERIFIED UNPRESSURIZED) UNABLE TO PRESS IN RED PUSH BUTTON ON MAIN CABIN DOOR HANDLE. HAD TO PUSH AUXILLARY LOCK BUTTON RELEASE HANDLE BEHIND MAIN HANDLE TO GET DOOR OPEN. /// CORRECTIVE ACTION /// REPLACED PRECATCH LEVER SPRING P/N S2952-46, AND REPLACED MIAN LEVER SPRING P/N S2952-64. REASSEMBLE PRECATCH ASSY PER MM REASSEMBLED CABIN DOORSTEPS OPS CHECK GOOD AT THIS TIME PERFORMED WORK IAW CESSNA 680 MM CH 52-10-4.