I just got a reminder from the BMW site saying i'm due for my 6000 mile engine oil change. When I went in at 3000 miles to the dealer, the dealer just added engine oil and didn't drain it out. Is that right? Also i called and asked them if i should come in for an engine oil change but they said it's unnecessary. I bought some engine oil. Should I add engine oil to it or go to some place to drain it out and add engine oil?