Murdered New Zealand woman Karen Ristevski's mechanic has made a chilling statement to police, saying there was nothing wrong with her Mercedes Benz.

Her husband Borce claimed that his wife's car had a faulty fuel gauge, so took it for a drive on June 29 last year, the day she went missing. He said he hit a bump in the road and the gauge corrected itself.

But the mechanic, who has been interviewed by detectives, debunked the claim and said Mr Ristevski had never raised the problem with him.

"In all my time working on Mercedes Benz cars, I've never come across this type of problem before," the mechanic told the Herald Sun.

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A Mercedes expert has previously rubbished claims the 2004 Mercedes-Benz SLK 200 coupe had a faulty fuel gauge.

Experts told Fairfax Media the car was "not an FJ Holden" and would not be fixed by simply hitting a bump.

Nick Theodossi, of Nick Theodossi Prestige Cars, said he had never heard of this happening in the 35 years he had been working with Mercedes cars.

Another mechanic told Fairfax there were two sensors in a Mercedes fuel tank, meaning both would have to be broken to give a false reading.

Investigators have named Mr Ristevski as the number one suspect in his wife's murder.

There is no suggestion he committed the crime.

Ms Ristevski, 47, went missing from their luxury $1.1 million Avondale Heights home in Melbourne's northwest after fighting with her husband about money.

Eight months after she walked out the door her decomposed body was found between two logs in bushland at Mount Macedon, an hour's drive northwest of Melbourne's CBD.

In December police conducted a two-day search for the missing mother at Gisborne and Toolern Vale in Melbourne's northwest.

She was found in February about 25 kilometres from this search area.

The search began after phone towers tracked mobile phones, belonging to Ms Ristevski and her husband, in the area.

Mr Ristevski told police he was driving Ms Ristevski's car in the area when the fuel gauge corrected itself. He claimed he did a U-turn and went home.

In July, police retraced the steps of the black Mercedes as part of the investigation.

In June police released new CCTV images that show a car they believe is Ms Ristevski's Mercedes.

The vehicle, which has Mercedes-manufactured five-spoke wheels, is pictured driving northwest along Old Calder Highway over a railway crossing in the northwest Melbourne suburb of Diggers Rest at 11.12am on the day she disappeared.

Police suspect the car may have been driven further northwest to Gisborne or Mt Macedon about noon the same day.

One theory police are working on is that Mr Ristevski was driving the car in Diggers Rest at the time the CCTV was captured and that Ms Ristevski's body was in the vehicle, according to the Herald Sun. The Mercedes was the last of six vehicles seen driving close together in the suburb.

There have been a number of bizarre explanations for Ms Ristevski's murder.

Mr Ristevski's son from a previous marriage, Anthony Rickard, claimed Ms Ristevski was going to leave her husband as they had been having an affair.

Following her disappearance, Mr Ristevski's brother, Vasko Ristevski, claimed she had fled the country on a fake passport.

Police said Missing Persons Squad detectives continued to investigate the death of Ms Ristevski and the investigation remained ongoing.