I have an Echo GT2000 trimmer that I use for my small part-time residental lawn mowing service. Everytime after I use it, I have an oily residue that runs out the muffler and then across the back of the unit and down the gas tank. My oil-gas mix is correct. I replace the air filter, spark plug and gas filter each spring. My Echo dealer advised me to run the unit at full throttle- that didn't work. He adjusted the carb., which also didn't work. He told me to bring it in and he would take a closer look at it. Has anyone experienced the same problem, and if so, what was the problem? Thanks.