I have used Shell 5W40, Motul 0W40, Redline 0W40, German Castrol 0W40, Ravenol 0W40 on my Mercedes SLK 1.8t.
Ravenol is available in a store near my work and quite a bit cheaper than the Motul, Redline and Castrol, except Shell whose manufacturing plant is in same city as me.
My gf who know...