Saboor bhai with due respect i read following from a westren website & same happened to me in my cultus efi;
Synthetic OILs got a bad reputation for leaking. This was because, despite the claims of the oil manufacturers, the seal-swell characteristics of the new synthetics were different from those of the mineral oils they replaced. If the seal-swell rate was lower, the seals shrank and oil leaked from crankshaft seals and rocker cover seals. If the rate was higher, the seals swelled a little extra and the engine was tight. Then if the owner changed back to mineral oil, or added a quart when no synthetic was to be had, things got really bad. The crank seals had become worn, in their turgid state, and then relaxed. The valve cover seals were compressed when swelled, and when the different oil was added, everything leaked like a well.