Chineses cart, Terminator, looks like the Explorer II, 150cc, at the back of the plastic housing on the left side it says "Oil .11 liter", I see what looks like a drain plug at the rear of the aluminum housing on the bottom, but where or how do you check the oil, and where do you add new oil if you change it? Do you have to remove the plastic housing or do you add oil thru the vent tube hole? Thanks.