I have run DELO in all my other Mercedes for the past 12 years. I just hadn't made the switch in the E320 yet. I prefer DELO for its superior detergent qualities and zinc additive lacking in conventional motor oil. I wonder if the detergent broke something loose which is now obstructing an oil passage? I think I will leave it in there for now and see where the ticking goes. One of my 380s ticked like that for 3 years and never got worse. It was just a little annoying.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280