Aray Bhai, bataya to hay kay oil level check karo, ager theak hay to sirf blowing problem hay. But since engine will be required to open and compression ring has to be changed. Out of three cylinders only one may have developed this problem. However since mechanic will charge the complete fee either you change one ring or all six, therefore get your all rings changed (one ring is around Rs 100). Plus he will change
a) "Master cylinder head gasket"
b) engine oil
c) head gaskit (also called tappet cover seal)
Therefore it will be kind of mini overhauling.