I have a problem with my FR131T, the drive between the engine and the cutting head disconnects occasionally, it seems to be where the flexible drive shaft joins the solid shaft somehow.
I have one of these and I love it. When I ordered it from my Stihl dealer he had never heard of it! He didn't know Stihl made Backpack brushcutters. The only weakest link is the flexible shaft but I always keep a spare.