Why would you opt expensive engine oil without removing the cause of oil reduction ?
Or you BELIEVE that feeding expensive engine oil will automatically rectify the oil reducing issue?
By the way, the dip stick is just showing a quarter liter less oil.
(Insight : Lowest & Upper level of dip stick is designed for 1 Liter gauge. If oil level on dip stick is at middle
between two points, it means Half Liter is less).
If you don’t know which oil previous owner was using, then simply top it up with any mineral oil like 15w-40 or 20w-50 (just for top up purpose). And carefully observe the level every day.
If it reduces again, then find the cause first.