You should definitely change your S/C oil every 30,000 mi or 36 months. It's a 10 min job tops. Use an old hand soap pump (rinsed out) and suck out as much old oil as you can. For the love of god, don't get any of the used oil on your hands! Refill with approx 8 oz (2 bottles) of new GM S/C oil (part #12345982). Fill until you see oil at the base of the filler hole threads and seal her back up.