My Santro Xing 2005 has done around 60k kms now; it gives me about 11-12 kmpl with AC always on. However the car is in good condition, the gear sometimes struck n the clutch feels very hard while driving. When I took my car for service the service advisors told me that there is a need of engine oil substitute plus oil filter, engine flushing and also there is a need of engine decarburizing imagine that it is part of 50000 km service. i want to know is that my car really needs engine decarburizing and would carbon cleaning help me increase my mileage? If yes how much would it cost?