Yes. You will have to get a hex from that axle manufacturer that fits that axle and the inside of the rim. They may have a total differant way to drive the wheel.
We may never know what fixed his issue but I see your point about the hex being the issue. I will agree locktite should be used on the set screws for the hex (secure the hex to the axle) to keep them (and the hex) from coming loose. Locktite on axle threads is extra insurance but a serrated lock nut is all that is needed when you feel hardly any resistance when securing (tightening it on) a lock nut time to change it out the nylon (or whatever it is) insert that acts like loctite gets worn out.
Register and gain access to Discussions, Reviews, Tech Tips, How to Articles, and much more - on the largest ECX RC community for RC enthusiasts that covers all aspects of the ECX brand!