simple fix err no not simple take the top plate off the gearbox and fish it out. you can just get at all the bolts throught the vch. it possible to to do insitu but everytime i`ve done this it meant dropping the props and then the gearbox and spending a couple of hours with a claw or magnetic pic up tool trying to find the ble**ing thing. it sounds as if its got stuck between the gears inside the box.

good luck just think its a bank holiday weekend you needed something to do !!