My experience of the 1.9 cdti lump is limited to one Vectra C manual, that car managed 36mpg over 25k, and was in the workshop for warranty work every three weeks, which was mostly engine related, hence my distrust... three 1.8 Vectra Cs and about 300k between them and consistently averaging 32-35mpg, not a single engine issue except for an intermittent fault light for the variable valve solenoid filters on the Z18XEV. This took a whole ten minutes to fix
(Thanks to MrDTM for his guidance
).
The pence per mile is near enough the same petrol vs. diesel, and petrol offers the possibility to fit lpg.
Servicing the 1.8 is a piece of cake too, and costs peanuts...