Please don't use oil of standard less than API-CH4.
I don't think Servo has a product that is CH4+.
I would suggest you find the biggest oil distributor in ur area and source Castrol GTX diesel 15W40(API-CI4) or Mobil Delvac MX 15W40 (CI4)
Both are API-CI4 rated. I've used the GTX diesel twice and Im pretty satisfied with smoothness and the oil ageing. I can't give detailed reports since Im yet to find a facility which does UOA (Used Oil Analysis) and God knows how much it would cost.
I drive a Petra 1.6 in Bombay. During the last service, I changed to Mobil 1 0W40 grade oil. Many on the forum had warned about this oil being too thin for our tropical conditions and that there would be regular top ups required. So, I got a litre of additional oil for such an eventuality.
Thankfully, the oil level is unchanged to this date. I have driven about 5500 km since then mostly in heavy stop and go traffic, as well as a little on highways. So, perhaps, one need not be as worried about this oil evaporation as its been made out to be.