The VIN will tell you whether this car is:
1) An engine transplant victim,
2) Misrepresented.

There is no 3. a 500SEL (w126) has a 5.0L M117 V8, there is no 5 liter Diesel. There was a 3 liter Diesel w126, the 300SDL. This car might be a 300SDL. The VIN would tell you that. The VIN would tell you if it was an original 500SEL as well. But if it now has a Diesel, the VIN will not tell you what Diesel is in it, and how well or poorly the swap was executed.