Ten reasons you need this Merc 300SL

There is one reason why you should pay attention to next month's RM Auctions sale in Monaco, and it isn't because Sir Stirling Moss's old 1956 Maserati 450S Prototype is expected to fetch over £4 million. It's because there is an incredibly rare, incredibly desirable Mercedes 300 SL Gullwing up for grabs.

Oh sure, the old Maserati is a beaut: originally a six-cylinder Works racer with coachwork by Fantuzzi, driven at the '56 Millie Miglia by Sir Stirling and Denis Jenkinson. Once its business at the Mille was done, the Maser returned to the factory where it become the prototype for the new eight-cylinder 450S.

It's the first time the Maser has come up for sale in 33 years, and is expected to headline the big Monaco sale.

Which is all fine and dandy, but there's another car crossing the block that got our attention. A Mercedes 300SL Gullwing. This is no ordinary Gullwing, however. It's only one of 11 cars to be picked and sent back to AMG for a light tuning. We're talking modern running gear and an updated chassis, a restored interior and that bodyshape that crippled many a thought over the years.

It's estimated to sell for over £600,000. Here are ten reasons why you should take this 300SL Gullwing very seriously indeed.

According to AMG project manager Volker Niewig, you have the Royal Family of Brunei to thank for this gem. They originally put in the request to Mercedes and AMG to build a retro-modded 300SL. AMG said yes, and built 11 of these bespoke Mercs between 1996 and 2009.

As upgrades go, you can't really best an AMG V8. AMG thought so too, and fitted its own M119 6.0-litre behemoth into this little 300SL, an engine that featured in some of the rarer AMGs (SL60, E60). In fact, the M119 was, in turbocharged 5.0-litre form, the heart of Merc's C11 Group C racer.

Here it produces 380bhp, and pushes the Gullwing onto a limited top speed of 155mph. Best to think on that for a moment.

This 300SL keeps the original W198 chassis, though slightly modified to accommodate that monster 6.0-litre V8. In order to put the power down without exploding in a ball of expensive 1950s metal, AMG binned the Gullwing's swing rear axle setup, and instead installed the R129 SL's rear axle assembly. That's the 1990s Merc SL. There's also a Bilstein adjustable sports suspension pack installed, and power steering up front.

While it's got rear brakes from the W124 E-Class (that's the one built between the mid-Eighties and mid-Nineties), the 300SL uses the front brakes from the C36 AMG. That was the first car to be jointly developed by Merc and AMG, fact fans!

A brief history of the Mercedes-Benz C-Class

Recaro sports seats, three-point seatbelts, a leather wrapped steering wheel, air conditioning, and a modern stereo with a six-disc CD changer and an iPod connection have all been installed. There are also new AMG wheels with low profile, high performance tyres, and electronically adjustable side mirrors. It just keeps getting better.

Of the 11 300SLs built, five were completed for the Royal family of Brunei, while the other six were to delivered to - and we love this bit - ‘qualified customers'. Eight were coupes, with four of these being right-hand-drive, the other four left-hand-drive.

This particular car was built in 2001 and originally purchased by DD Racing in Germany directly from AMG. In 2005 it then moved to a collector in Hong Kong, where it has remained since, being stored in a climate-controlled garage.

All the cars were built to individual customer specifications, but Mercedes and AMG never bleated about the project, nor have either expressed any interest to do it again. And with so few 300SL Gullwings left on Earth, we suspect these 11 might be the first and last.

It works. It's been recently serviced by SPS Automotive Performance, and since its conversion by AMG, has covered just 300 miles. So it moves and everything. Quite fast, we're guessing.

OK, we're not entirely sure the wheels are the right fit for this car, but come on, the 300SL Gullwing is gorgeous. Arguably the world's first true supercar, Mercedes' crowning design achievement and a Hollywood favourite, it's a very glamorous Thing. Now it's got the heart to match.

RM will auction this next month in Monaco. We suggest you find a lot of money and head down there.