Well, that narrows things down a bit
.
you will generally be able to see if the pinion gear is messed up, there wont be much teeth left. (i can send you some picks of a new one and a worn one) (tonight)
But if that looks ok, then it could be a tooth is chipped off a gear in the mechbox and that piece is getting things jammed up and your gears are stuck.
At this point you gotta open the gearbox again
look for any chipped teeth and
make sure your bushings are properly pushed in. That is important, if one bushing isnt in properly it will jam things up, also be careful not to lose and of those little washers (shims). Make sure they go where you found them, because that will also make things jam up if they arent where they are meant to be.
But it might not be the pinion gear anymore. Something is jamming your gears, either a chipped tooth on the gears, bushing not "clipped in" all the way, Misplaced shims.
Welcome to the life of AEG troubleshooting :x:
watch some youtube on how to put your gearbox together, it will teach you some tricks to make it easier on you when putting it back together