I have a early 90's craftsman tiller, selp propelled walk behind with a 5hp briggs. I have noticed that it has become hard to start, and when it runs, it smokes. I started thinking, and wondered about the oil... well, I cant ever remember changing the oil, so I guess it has 15 y/o oil!! But, I cant find a dipstick, or the drain plug, and have no idea how much oil it holds.... Just wondering, how much longer does it have?????