Diesels are very responsive to any change in maintenance you do, some signal of anything going wrong. With shell Rimula i had experience of oil getting so thick after 1500 kms t hat engine refused to turn over at cold start.
Changed to Delo withs ame filter for a while just to see what hapened, and it was all fine again with same tired battery. Used top of the line Rimula X as well but it gave up after 2500 kms. bubbles on dipstick and viscosity was non existant.
I think shell use a lot of recycled oil which they collect from the suction machines at pumps. They were the first ones to introduce that method of oil change and i am damn sure that oil collected is recycled, Have heard of some factory near multan where all this is done.
Also, most shell pumps are contract operated, not company operated and temepring is very common so i do not take rsik. Its been 12 years now that i havent used any shell lubruicant. Caltex, ZIC, Total and now Petromin.