For a period of time European Cessna aeroplanes were built under licence by Rheims Aviation in France. All were factory corrosion proofed during the RA building process as a standard. When a Cessna was imported from the U.S. it was of concern that corrosion proofing hadn't been done. If it hadn't and following inspection the aircraft was clear it would then be thoroughly treated with wax oil. If it had corrosion you were advised to walk away.
Some U.S. imports had been factory treated; my understanding was that factory corrosion proofing was only an option on order.