Wobbly (Not Nodding) Head issue

[IVGavordny]

I have a relatively new BT3, and I find that her head has become loose - not the "nodding" problem as reported, but the opposite - her head is swinging back and forth. I've pulled her face off (!) and popped the foam "skull cap" ("Paging Dr. Lecter, Dr. Hannibal Lecter...") and found that the bolt on the "floor" of her skull case has loosened. I've tightened it up with an allen wrench several times now, and it keeps backing off as her head is moved from left to right. So....

1) Any idea on how to fix this so that repairs last longer?

2) I pulled the stack of washers that fit in the top of her neck. Does somebody have a diagram showing how they should be ordered and oriented?

3) Any recommended improvements? My first thought was some kind of stack using serrated washers, so that her head would "index" back and forth.

[Dorean]

If the bolt keeps loosen, try some lock tite glue for nuts and bolts.

[young guy]

I see this thread is pretty old, but it's the most recent thread I could find referencing this particular problem. Hopefully, this is my last newbie post, so I can now start a fresh thread with some pics. Everyone I have seen on this site has seemed to be so friendly and helpful, I hope to be able to contribute in a meaningful way.