Red Loctite does have a lot of strength, but I don't know if I would be comfortable using it to retain a bolt that doesn't get torqued very tight to start with and is subject to some considerable stress. I would try to find out what is wrong causing the extra clearance in the stub axle. Maybe an incorrect part was installed from factory if it has never been apart. Can you post some pictures of the final drive, stub axle, and diff lock parts? How much clearance is there to allow the retainer to fall off?