Hi recently purchased a 1990 sel mercedes- benz and I was wanting to know what type of oil do I need to use for it? And also what type of gas should I use for it? regular or diesel.

Mobile one oil, is best for mercedes,and if you have not added gas to this car dont,this model does come in diesel and regular fuel,and i have no way of telling you which one it is,and you will damage engine with wrong fuel,before you add gas to car find a good mechanic to tell you it is deisel or regular fuel,dont damage the engine.

Fuel type should be marked inside the fuel door and also on the fuel gauge. I also agree Mobil 1 is what I used in my Mercedes.

You can't tell the difference between a gasoline and diesel engine? You haven't looked at the operating manual? Buy a bicycle.