Liz, welcome to the "club". You can go to any Mercedes dealer and buy an owner's manual. I was able to get one my 1980 300SD, it took about 2 weeks and cost only $15. It is a reproduction, but the fact that they still had one available, is impressive. Oil, ohhh the old oil question. I won't go into brands and such. As it has been mentioned above, this subject has been beaten to death. That doesn't mean you should feel bad for asking. there is a search function you can use. When you get a hold of an owner's manual it will tell you what is best for your climate. I do strongly recommend you not go to Jiffy Lube or the alike for the same reason you cited. Yes Mercedes take alot of oil, my car has a 3 liter engine, yet it has an oil capacity of 2 gallons (8 quarts). The "monkeys" at Jiffy Lube would only assume 5 quarts. As for what type, by that do you mean brand or convential oil vs. synthetic?

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member