The Air Force's 17 mothballed Skyhawk jet fighters are being damaged by being kept outside, the Government has confirmed.
The Skyhawks were decommissioned by the Labour Government in 2001 and are waiting to be sold.
They have been stored with a protective covering in the open at the Woodbourne air base, near Blenheim.
However, associate Defence Minister Heather Roy said the aircraft had been damaged by the weather.
"There is a little deterioration but no more than you would expect under the circumstances," she said.
Since the Skyhawks were moved out of a hangar and into the open in December 2007, the previous Government said the protective latex coating had worked and there had been no damage from the elements.
The Skyhawks were sold for $155 million to an American company but the sale had been held up by the US State Department, which must approve any sale of aircraft with American military avionics.
The Skyhawks may be old but they had been fitted with modern avionics, similar to the avionics in American F16 fighters.
The Skyhawks were to have been replaced by F16 fighters and a deal had been agreed to by the National Government before it was ousted at the polls by Labour in 1999. The new Labour Government axed the deal.
Last October the Air Force said rainwater had got into four of the 17 Skyhawks.
Parachute packs got damp and some instruments were a bit wet so components were removed and serviced.
The Air Force said there was no damage or impact on the sale or resale value of the aircraft.
In August, then defence minister Phil Goff confirmed some of the latex protective coverings had been torn in a storm but there was no damage.
Defence Minister Wayne Mapp said the sale of the aircraft was "progressing".
"That issue is largely going through the State Department and the Defence Department in the United States. It's an ongoing process," he said last week.
The delay of nearly seven years in the sale of the aircraft was the work of the previous government, he said.
"Frankly when they said they had been sold they did not really say there was a whole lot of conditionalities around that. You have also had issues with the change of administration," Dr Mapp said.
The Air Force's 17 Aermacchi training jets had also been on the market since 2001 but they were regularly flown to keep them airworthy.