We just acquired a like new Troy-Bilt Pro Cut lawnmower with a Honda GCV160 5.5 engine. It was barely used and the oil still looks like new, apparently it was owned by an elderly couple that had lawn service instead. My question is this, how do you change the oil in it? I found the dipstick but there's no drain plug underneath by the blades, any ideas? Also, does it use SAE30, and how often should I change it? Thanks!