Thank you all for your replies.
The plug was a bit fouled.
I used to drive around 160 kms/hr but now they have radars all over the highway limited to 120 km/hr.
City driving would be 60 - 80 km/hr and freeway driving at 120km/hr.
I travel daily total 90 kms to work. i:e 45 each way.
So I believe I should find some H9DC or H9DCO plugs.

The summers are quite hot here averaging 40 to 45C. Would that affect the sparkplugs choice by any way.

__________________
300CE 1989 Euro Model.
ML350 2011.