My E230 MERC consumes about 1 liter of Engine oil for every 1500 kms of mileage. I top up the spent oil regularly but am quite concerned about the oil consumption. Please advice what could be wrong. Does anyone think the engine needs a overhall?.

Also i get a creaking sound from the front left wheel side when i turn the stearing wheel. I have tried lubricating ( randomly) the front side behind the left wheel by using WD-40. It works .. but only for sometime. The creaking sound returns back. What causes the creaking sound ?