I had a FS100RX trimmer and had problems from after about 3 months. Over the next 3 seasons the dealer did a ton of warranty work on it, you name it they replaced it. They gave me a loaner each time they had it in. Ended up after everything had been done, it was out of warranty and still not running correctly. Worked out a deal with Stihl to trade it in and get a new one at a very reasonable price. I have had the new one for about nine months and here we go with this one. And on this one I have used the Ultra Oil in it from day one. The dealer has had it several times over the coarse of the last month and a half, replaced everything on it just about and it runs worse now then it did when I took it in for the first running issue. Needless to say they have it again and I think it is time to just buy a different trimmer. Thinking about RedMax, Shindaiwa, and Kawasaki.