I just looked at my Trail Boss and realized that the lines on the oil cooler are on the top. When you drain the oil out of the crank case is there still oil left in the cooler? I bought this a few months ago and not sure what oil is in it. I was going to replace with Mobil 1 synthetic oil (read that on another post) and wasn't sure about mixing the oils. Any input would be GREAT! Thanks, Greg