The MB dealer (and my local parts shop) sells a special MB additive which sells for around $12 per 100ml. It's apparently a cleaner and octane booster and one capful is good to treat 40 litres. No idea what's in it as there's no label on the bottle but its brown and quite oily. Been around for a while and I think its to do with the fact that the local petrol has always been fairly low octane, 88 I believe. Unleaded fuel with 95 octane rating was introduced in the last few years but good old leaded fuel is still 88 so maybe it's to compensate for that.

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1987 300e manual 250,000 km (sold)