I would suggest it would be one of these - mislabeled.

They are not so rare. 450SL convertibles are more expensive.

http://www.uniquecarsandparts.com.au/mercedes_450SLC_technical_specifications.htm

It has to be an idiot selling a 300CD. 275k, a second tank and a large dent? Starting price at 15 grand? What else could it possibly be? I doubt 450SLC.

__________________
1985 500SL Euro w/ AMG bits 130k
1984 300SD Turbodiesel 192k
1980 240D Stick China 188k
2001 CLK55 AMG 101k
2007 S600 Biturbo 149k Overheated Project, IT'S ALIVE!!!