Setting gear mesh is mostly only needed on the motor pinion to spur, and that's a piece of cake. I would say send it to me and I would fix it for you, but you don't have too difficult a problem there. Those screws are threaded into plastic right? There won't be loctite on them.
Take the arms off so you can get a bite on the screws. I assume you are trying to grab them from the end. That won't work nearly as well as gripping them from the side.