Engine Oil frequent loss. At the moment I am having bit of trouble regarding engine oil level in my Linea Petrol (1.4 Fire).I got my 3rd service done in the monthe of June 2011 to be precise and usual change of Selenia engine oil was done.I purchased the 4l pack and the car consumed 3.3L at that time and I kept the remaining 0.7L.I In the month of November I casually checked the engine oil level and to my surprise it was almost (90%) empty Then and their I poured in the remaining 0.7L of the engine oil and after few hours checked the level.Now it was almost upto the brim.At that time I didn't paid any serious attention to the matter.Again today after about 4 months I checked and the level and again the same thing happened.At the moment the engine oil level is critically low.AFAIK there is no leakage of any sort in the car.It happened a year ago also when I had to take the car to TASS where I got it refilled but the mechanic their could not decipher the real cause. Should I take the car to the TASS (which will require time) or refill the engine oil with Castrol Fully synthetic one since TASS will not sell Selenia like that I mean for normal Sale. Is this behavior unusual since car has run only about 5.5k kms after its 3rd service in about 7 months ? Will it be ok to pour Castrol in it without draining out the remaining Selenia from it ?