Being perfectly candid I think that you have created a rod for your own back by highlighting your oil consumption.
You are actually getting 1666 miles per 1 lt. of oil which is above what Nissan recommends as being acceptable. (depending on the model, year and mileage)
Highlighting the oil consumption numbers in your advert will definitely have an adverse effect on you getting the car sold.
I would rewrite your add accordingly, however, if any potential buyer asks the question regarding oil consumption, then be open and tell them the miles per litre.