I have a Toro Super Recycler Mower that has the 6 Horsepower Briggs & Stratton Engine, put in 1 ounce of Auto-Rx last summer and changed the oil at the end of the season, nothing unusual, put new oil in and added 1 ounce of Auto-Rx again, using Amsoil 4-Stroke Synthetic, changed oil today and it came out black, will not be using mower again until next Wednesday, should I put the Amsoil in with 1 ounce of Auto-Rx or should I get some cheap dino oil and fill the gas tank up and let it run for an hour to do kind of a rinse, this mower is 11 years old and I mow a few yards for people with it, I am guessing since 1998 I have put over 1000 hours on this machine, mower is running great, just surprised that it took until I changed the oil a 2nd time for the color of the oil to be very dark.