I have been using an FS 76 FS76 for a few years now. During the first half of acceleration it seems to have developed a shudder (bad vibration) after it is wide open it seems to run fine, but it is slow to accelerate and clearly isnt running right. It runs fine without the gearbox attached. Does anyone have any suggestions? Where can I get a gearbox? Also, what do I need to attach a blade to this model? I have the blade but to I need a special screw or mounting kit?