That engine, I think, requires MB Spec 229.3/229.5.
The Mobil Site says to use the new M1 FS X2 5W-50, or second choice is M1 FS 0W-40. You are OK if you use the new versions of those, since they are the new Full SAPS M1 oils. (I have two MB cars with same spec requirement).
For Castrol, they say to use their 5W-40 A3/B4, which is MB 229.3 compliant.
If you are using one of the MB-compliant versions above, you should be OK.
I would use the M1 5W-50 in Hawaii.
I would not try to use a one-oil-fits-all version. Having two types of oil is no big deal. Get the one that MB certifies for the car.
For example, I have to have Full SAPS for 2 old MB cars, Low SAPS for the diesel, and 5W-30 for the Ford. Breaks up the boredom!
Is there any reason why I shouldn't be using either M1 or Castrol 0W-40 in my 1995 E320 / W124 and M104 engine with 223k miles on it?
What are your suggestions?