My 1958 4 cylinder 190 Ponton was built in Stuttgart with fuel specified: " petrol unleaded". Apparently the 6 cylinder 220 Ponton fuel is specified " petrol premium unleaded" I've been told many many times about owners of W123s, W116s and W126s all being astounded by the way their cars markedly changed for the better after using at least one tankful of premium unleaded - prior to which their cars were not smooth starters and runners whilst previously on continuous use of the cheapest (low octane) petrol.