Idea struck me yesterday when i fired up the gas powered edger, I'm sure this unit is seriously sludged. About 10+ years old, gets run maybe 15 min every 1 to 2 weeks, I thought "what a perfect candidate for my newly arrived Autorx'. still starts on the first pull, but it went thru several season in the past without changing the oil. So how long do you think a treatment should be left in? I figure dose with an once and leave in all season then change again at the end?