After buying; refurbishing and reselling a Beech Baron 58P; an FBO Co-owner was informed the rudder trim cables had been found reversed; even though the aircraft had flown many hours without any reported rudder trim problems.

Narrative

REVERSED RUDDER TRIM CABLES and CORROSION IN ENGINE:I purchased this aircraft for the purpose of refurbishing and selling the aircraft. I was notified thru e-mail that the rudder trim cables were hooked up backwards after the aircraft was sold and flown approximately 2000 miles to ZZZ.This aircraft was bought after sitting approximately 10 years. It went thru an extensive refurbishment. This refurbishment included the complete overhaul of both engines. Both crankshafts were sent out for overhaul. The left crankshaft was rejected and a used 'overhauled' crankshaft was installed. Earlier this year; an Annual Inspection was completed and signed off. The aircraft was test flown by a hired Pilot/Broker and no cable reversal was reported. The aircraft went thru a pre-buy Inspection the following month and no cable reversal was reported. The aircraft was then purchased and was flown back to ZZZ1. The aircraft was flown for a week after that with no problems reported. About one week after being flown back in ZZZ an oil leak was noted on the left engine. After changing both the prop governor and prop seal it was taken to an FBO and the left crankshaft was reported cracked. Photos were forwarded. The engine was disassembled and extensive corrosion was reported to be in the engine. At this point the right engine was disassembled and corrosion was noted in the right engine.This aircraft was stored in a heated hangar the entire time while going thru refurbishment. After refurbishment it was stored in a heated hangar. It was at this point during engine teardown that the mechanic noticed the rudder trim cables hooked up backwards.I have reviewed our Inspection worksheets and could not find when or why the rudder trim cables were disconnected or even if they were. But according to the E-mail I received from buyer they were. The aircraft going thru such a major restoration should have gone thru a much more rigorous Post Inspection and all Flight Control Cables and Trim Cables should have gone thru an Operation Check with another mechanic watching for proper deflection and operation. Procedures were not followed after an Annual Inspection by performing Operational Checks.I am Co-Owner in this company and although I was not the Mechanic who performed the work; I should have made sure proper procedures were followed and company policy was adhered to. I also believe a Detailed Checklist for the Test Pilot might have caught this problem prior to the aircraft being released for service.