Just got my first service done on a brand new 09 Si Sedan. I love it to death and it's driving fine, no tranny problems. When I got home however, I noticed that the bill for the oil change was only 27$. This doesn't sound like they used Synthetic oil on my engine and it's too late to call and ask. Is it absolutely imperative that they use synthetic oil or is just better? Should I go get it changed if it isn't synthetic?