Rainwater has got into the cockpits of four of the 17 mothballed Air Force Skyhawks stored at Woodburn Air Base in Blenheim.
The Government says it is a small amount of rainwater and there is no damage to the aircraft.
Cockpit seals have been repaired and Defence Minister Phil Goff says there is no impact on the sale or resale value of the combat jets.
Dampness was also found on some components, which have been removed and serviced.
Two American companies have agreed in principle to buy the planes, but the United States government must give its approval before any sale can proceed.
