As has been said before, the words "premium", "regular" etc have little
meaning. What matters is the actual octane number. I guess there is no
manual with instructions?
I would follow the manufacturer's instruction. Do you think your gauge sign
was applied by Merc?
I have a 1993 190 E 2-litre and it runs on 95 octane unleaded, equivalent to
about 90 US. (I had timing changed by dealer when nearly new, just when
unleaded was coming into the UK in a big way.)
NB: To reply directly replace "nospam" with "schmetterling"