Well this is probably one for the Losi experts as I don't really know enough about how these parts are supposed to fit together.
Perhaps there is a manufacturing fault by Fibre-Lyte?
Either way I wouldn't want to slot parts as that will weaken them and/or make the fit less secure.
By the way you can also get ball nuts which will let you thread a longer screw from the other side without needing to hunt for a long thread ball stud. Kawada make quite a variety of metric ball ends, available through Much-More UK -
http://www.muchmoreracing.com/store/...ex&cPath=4_108