Forget running anything 20 weight where you are, especially with the extremely high levels of sulfur in your gas. Skip the API/ILSAC ratings, go straight for an ACEA A3/B4 oil. Off the top of my head, I would suggest any of the following:
- Genuine AMG 0W-40 (from your Mercedez-Benz dealer)
- Fuchs Titan SuperSyn 5W-40 (Made in Germany, not the Alhamrani-Fuchs version made locally)
- Liqui-Moly Synthoil High Tech 5W-40
- Liqui-Moly Leichtlauf High Tech 5W-40
- Shell Helix Ultra 5W-40 (Made in Oman, which is the GTL version)
- Mobil 1 0W-40 ("Made in EU" not "Made in Egypt")
- Delphi Prestige Plus 5W-40 from your GM dealer (Made in France, skip anything else made elsewhere)
Stay away from Castrol or any other oil blended in the UAE. I'm sure you have a variety of Petromin oils available as well. I have not tried them, and I am quite skeptical of them because of inconsistent labeling - e.g. their 5W-30 "Super Synthetic" "meets" API SN and ILSAC GF-4 (GF-4 not GF-5) but also "meets" ACEA A3/B4 along with BMW LongLife-04 and GM Dexos1 in addition to VW 502.00/505.00. It doesn't list them as "Meets the requirements of" but actually "meets". How that's even possible, I do not know because those are some very different specifications. Stick with European sourced lubricants if at all possible.
Stick to an absolute maximum of 5,000 km drain intervals. Do not blow your air filter out with compressed air, change it out every second oil change/10,000 km).