Nice work. Looks like that oil needed changing... it appeared very dirty on the pics, considering its a petrol car. Have you ever considered using an oil flush? Its not a high mileage car, so shouldn't cause any issues. I know garages that use it all the time and never had a problem. It works wonders that stuff.
With regards to oil, Castrol has always been really expensive. I prefer to shop around and use other brands. So long as the viscosity and spec matches what's recommended, you can use what brand you want. Shell are very good, as are Petronas. I'm not sure if they do the exact oil for your car, but I figured if Petronas is good enough for an F1 car, its certainly good enough for my D5.
Its definitely worth shopping around. You can get good quality oils at a fraction of what Castrol or the dealer want.