I found similar with Perry's in Aylesbury on a couple of occasions. The main one which beggerd belief was the week after I picked up a used 166 V6 - check it for oil and there was only just oil on the dip stick.
I spoke to Perry's and was assured that the car had been given it's predelivery check etc - so it uses 5 litres of oil in a week? (about 200 miles that week)
Needless to say they were as much use as a one legged man at an ass kicking contest! - there response being basically tough!!
Thankfully the car was fine and at 69K i traded it in for a 147 JTD Multijet (middle aged mediocirty

)- I miss that 166 - but now I've got a GT