Hi, have the same problem, gear wheel inside box has stripped and therefore cannot get the drun off because it just turns both ways, this is what I did !
removed motor from back and then once I removed some metal frame from the cart with an angel grinder got to the bolts that secure the gearbox to the housing, once this is done got inside and saw knackered cog, cut slice out of it with grinder so I could then use hammer and bolster on cog, anticlockwise, job done, good luck !
nigel54321, August 2011