Here's another comparison for you .
Diesel $3.72 / imp gal , plus road user charges just for diesel @ about 2.2c / km. for the under 2ton / 2 axles.
Petrol $5.68 / imp gal.
The 300D does about 29mpg and the 300sel does about 22 if I keep my foot out of it
.
You can guess the diesel is the one that gets the 30k miles / yr on it .