Which Oil is best for my Tuscan S?

[tigerruss]

I was told that initially my Tuscan S (and probably all other TVR's) would come with a normal NON-synthectic oil installed e.g. Castol (Apparantly it helps the running in), but that this would be changed to Mobil 1 at the first service. Well I've had the 1000mile service but no mention was made of Mobil 1, instead the invoice shows 5ltr of Mobil Super 15W/40. Is this right? Is this a synthectic?

What do other people use?