some have suggested super glue on that particular grub instead of thread locker. It seems like it would do the trick and do it well, just don’t crank down too hard with that tiny hex wrench or you’ll strip the wrench, or maybe the grub. Then you’re fucked if it comes loose again some how.
This happened to me. I just removed the grub screws, pretty sure they are M4, and replaced them with a couple m410 or m415 (cant remember) socket cap screws so I could use a larger allen key to get more torque to lock it down realllyyy good, and threadlocked. The socket cap screws ALLLMOST dont fit, the head of the screw rubs up on the motor a bit when it first goes in but nothing crazy. Might work for your motors as well if you want something a little bit beefier than some grub screws to hold your shaft in place.
Thanks for all of the suggestions and help! I really appreciate it!
I ended up unscrewing the bolts that hold the shaft in place, put some loctite 648 down in the hole, turned the motor a couple of times, loctite 648 on the screws and screwing them back in without over-tightening them.
It doesn’t move anymore so seems to have fixed the problem