I would assume that old diesels, well diesels in general are stolen less per 1000 diesel vehicles vs the number for gasoline vehicles. Most people don't know how to start a modern diesel in the first place. The average person wouldn't know you have to let the glow plugs heat up before you can start the engine. Throw in a manual transmission and thieves are even more confused. W115 240D with a gorilla knob and a manual transmission would be a tough one for a thief to figure out.