The odor was gone for about six months, but than gradually returned to the same pungency by June 2013.

"It smells like melted crayon," he says.

Some Benz owners have had the air inside the vehicle tested and found high levels of benzene and formaldehyde, both cancer-causing chemicals.

Not in Sun's case. Tests showed the air inside his car contained safe levels of benzene and formaldehyde. But his doubts remained.

"The smell is so strong. There must be something else in the air," Sun believes.

Sanloulouzhang claimed both he and his daughter got pneumonia after he bought the car. "I was hospitalized last year for pneumonia. After that, I have seldom driven the car," he wrote.

The response from Mercedes offered little comfort.

A statement released last July by the company gave "sincere apologies" to affected C-class owners.

"We reconfirm that this condition (referring to the unpleasant smell) will not harm drivers' health, neither will it have negative impacts on vehicle performance and safety," the statement said.

The company attributed the odor to carpets, which it vowed to replace free of charge.

At present, the company offers to replace the car's carpets and clean the interior for affected C-class owners, a customer assistance employee at Mercedes-Benz (China) Limited told Xinhua when answering a telephone call on Wednesday.

The company confirmed the employee's answer in a written reply to Xinhua's interview questions Thursday, saying it have contacted affected users to replace carpets and clean cars since mid-May 2013.

"We have sent technicians and after-sales service personnel several times to conduct face-to-face communication with customers concerning the peculiar smell's source and solution," the reply statement said.

Not everyone is convinced by the company's blaming the carpets, as the replacement in both Sun and Sanloulouzhang's cases failed to eradicate the smell.