a little rat tail file work on the holes to clear them of exessive paint works well,I even had to open them up a bit to get them to lock properly there is a bit of paint build up around the holes to be cleared out, so the plastic knobs pop into place,its also good to make sure your putting the gear in the right side when installing them its easy to get them turned around,as well the paint can be exessive on the ends of the gear so one will lock but the other one won't.
I blew my gear out a few times the fix is pretty easy just part mof the hobby,little details.