Oil viscoscity is another hot subject. For years I used 20w50 Castrol in everything. Being in Florida, it fit in MB's chart.
Over the last decade I have read much that says that the largest source of wear in a motor comes in the first instances before the oil pressure is stable in the motor on cold starting. Based on these findings. it is widely recommended that light weight oils be used as they fill quickly and the pressure is stabilized more quickly. We have been using 10w30 Mobil 1 in cans untill we get a 55 gal drum. I think we will use 15-40 after that. We then will have three types of oil: 20w50 dino, 10w30 synthetic blend, and 14w40 Mobil 1.
Bosch Master, ASE Master, L1
33 years MB technician