I have a 92 Dodge w/ 2.5 four banger (152k miles). It has gradually been using oil, now consuming a quart of 5w30 conventional every 800-1000 miles.I change oil and filter every 4500-5000 miles. Since I am renewing the additives regularly, can I extend the oil change to 6000-7000 miles? I drive a combination of highway and city driving around 1200 miles a month.The oil does not look overly dirty.