Ahh... everybody encounters this. Not only on ML's but also those DC direct knee joints.
And yes superglue is the most basic and most effective method to tighten joints. Us customizers really have to know this part and we'll gladly share it to tou guys.

From Jin Saotome:
What you need: Super Glue and water.
What you do: Apply a drop of super glue into the joint. Work it around so it's all inside there and so it doesn't instantly set up. Then pour, dip, or drip water into the joint. Move the joint while you're doing this. The super glue instantly crystallizes into a matte-clear substance and expands, filling the joint. Let it set for about 50 seconds and then test it. A couple crumbles of dried glue will come off and the rest will be tightly adhered to the sides of the joints. Blow into the joint to get any water out afterwards.