Rare Mercedes-Benz revealed

A rare Mercedes-Benz that could be Australia's most valuable car has been unearthed at Melbourne's Motorclassica show.

The 220SL is one of four six-cylinder prototypes built by the manufacturer, and the only one believed to be in existence.

The roadster was the only example built in right hand drive, with a six cylinder engine that took the place of a four cylinder unit used in the similar 190SL roadster.

Retired Mercedes-Benz dealer Ray Eastwood reportedly took the priceless car as a trade-in without realizing exactly what it was.

David McCarthy, a spokesman for the manufacturer, says the renowned Mercedes-Benz museum in Stuttgart is aware of only one surviving 220SL, the very car that resides in Eastwood's collection.

The model is one that collectors around the world would pay a premium to own - potentially with a value over $2million - but it is not for sale.

"My feeling is that it would be a six figure sum at the very least," he says.

"It would certainly be one of the most valuable cars at Motorclassica if not the most valuable."

The show is stocked with near priceless machines including a vintage Delage roadster, classic Lancia Stratos coupe and an original Shelby Cobra 427 that spawned thousands of imitations.

Mercedes-Benz paid tribute to the 220SL with a special edition 2014 SL400 model that celebrates 60 years of the renowned SL nameplate.

It also unveiled its latest S-Class coupe, a flagship luxury car expected to cost around $400,000.