A 1938 Mercedes-Benz 540K Special Roadster is headed to an RM Sotheby's auction next month in Phoenix, Arizona. It is being offered up from a collection known as the Open-Touring Collection, and is scheduled to go under the hammer on Jan. 25.

The 1938 540K, which bears chassis number 408338, was originally sold with a Cabriolet B body, which meant it shared many features, including a chassis, drivetrain, lights, wire wheels, and instrumentation, with the more desirable Special Roadster cars which totaled around 60 units only.

This inspired one owner to change the body to the Special Roadster after the original Cabriolet B body came into a state of disrepair.

The new body was built by metalworker and coachbuilder Cass Nawrocki of Moose Lake, Minnesota, and took around two years to complete. Nawrocki had already rebodied an original 540K Special Roadster during a previous restoration job, and had the patterns and jigs to create another body, as well as a set of rusted original fenders, doors, and various other body panels to use as a reference.

1938 Mercedes-Benz 540K Special Roadster bearing chassis no. 408338 - Photo credit: RM Sotheby's

1938 Mercedes-Benz 540K Special Roadster bearing chassis no. 408338 - Photo credit: RM Sotheby's

With the body complete, it was up to Portland, Oregon-based Mercedes restorer Jim Friswold to rebuild the car. According to the listing, no expense was spared for the rebuild which took an additional three years to complete.

There were a total of nine body styles originally offered by Mercedes for the 540K. Production of the 540K together with the related 500K was handled at Mercedes' Untertürkheim plant near Stuttgart, Germany, between 1934 and 1939. A total of 760 chassis were built, with 406 of these being the 540K powered by the supercharged 5.4-liter inline-8. The engine delivers an estimated 180 hp and is mated to a 4-speed manual transmission.

The estimate for this 1938 example is between $1.75 million and $2.25 million. A fully original 1937 540K Special Roadster went under the hammer at a Mecum auction in August, but failed to sell despite reaching a top bid of $2.6 million.