BOSTON -- A small 50 cent part for your car could have a critical safety defect.

Team 5 Investigates reported Monday there could be more than 30 million of these parts on the road right now.

What To Look For | Photos: Spotting Defective Valves

Last November, Robert Monk, 31, died when his SUV flipped. Investigators blamed rapid air loss in the right rear tire. His family has filed a lawsuit.

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"There was a crack in the valve stem on his tire that led to a loss in air pressure," said Richard Newsome, an attorney for Monk's estate. "And when that happened, his tires failed because of the loss in air pressure. He lost control."

A valve stem is an inexpensive rubber part taken off the shelf and inserted into a tire so you can pump in the air. But a crack in the rubber could allow air to escape, causing the tire to deflate or rupture. You could then have a flat or a crash.

After the crash, the distributor, Dill Air Controls Products, warned service centers -- but not drivers -- about the problem of certain cracked valve stems coming from a factory in China. Another company using that same factory issued a recall for six million cracked valves.

But that number is insignificant compared to the 30 million potentially defective valves that Dill warns could be out there -- on any make, any model.

Initially, the problem was thought to involve only replacement tires. But Team 5 Investigates discovered it may threaten some cars bought new.

Sean Kane, a tire safety expert, examined the valve stems on our 2007 Ford Explorer. He found cracks on three of the four valve stems.

Team 5 Investigates then took our Explorer to Center Automotive in Needham for a second opinion.

"It's cracked all the way around here," confirmed Jim O'Brien.

The National Highway Transportation Safety Administration opened an investigation just weeks ago and is demanding a list of Dill's customers. But tracking potentially defective parts will be difficult because Dill admits in the warning to its customers that "there is little traceability on these stems after they leave our facility."

"We don't know where they are," Kane said. "We don't know how many cars have them. We know there are millions of them here in the United States."

Dill told Team 5 Investigates it takes these concerns very seriously and is conducting its own investigation. As for the cracked valve stems on our Explorer, Team 5 Investigates asked Ford for an explanation. The company has not yet responded.