what type of oil do I need to use for my C23O with 285k on it

5w-30 fully synthetic oil. always stick with what the manufacture recomended.

what type of oil have you been using all along??? factory spec is MB 229.3 5W40, 5W30, 0W30 or 0W40 in full synthetic

Mobile 0w-40 synthetic

use 20-50 good for tight engine compartment, synthetic are for newer models.