Thanks again to everyone.
JK, the service advisor informed that the brand of engine oil used is Castrol.ViscositySAE 15W-40 SpecificationsAPI CF - 4
Rechecked for the same on Castrol Website.
Castrol India - GTD#
I collected the vehicle back after 1st service at around 7 pm. My bill came upto Rs 2990. with oil (Rs 188 x 7.5 lt = Rs 1410.00), filter (Rs 182.00) changed, Engine flushed(Rs 759.00) and Bardahl new engine additive(Rs 478.00) added. The workshop GM himself emphasised on this. After all their contribution over the past 2 days I felt obliged and agreed.
On reaching home I took my family for a ride and dinner. Everybody was delighted that the saga finally ended soon on a happy note.