OFFLINE

This is my experience in tightening joints, more specifically to transformers. Do note that the what was applied for transformers might not apply to other toys because of the plastics used.

Therefore I'm not responsible for what happens, even for Transformers.

To tighten G1 toy joints.
1. Get some superglue - (fast dry one), or alternative is tamiya clear acrylic
2. Dissemble the joint.
3. Apply thin (sparingly) coat if tamiya type - with the brush. If using super glue - try taking a tooth pick and apply. Ensure it is even and not too thick. Usually I apply to the round ball rather than the hole itself, as it's easier to see whether you've applied evenly. If it's still loose at least can reapply.
4. Wait to dry.
5. Reassemble.

To ensure stickers (esp G1) does not fall off. Also can be used to protect stickers from fading.
1. Same tamiya clear acrylic.
2. Use the available brush and apply a thin coat over the sticker that has been applied. Best if you apply this on newly applied stickers - G1, G2, TF Prime Takara .. you know those kind.
3. Apply also a thin layer so it covers the edge of sticker to the plastic.  (Remark: DO NOT brush the stickers too many time and DO not use a blob of acrylic clear over the sticker. You might case the paint stencil to smudge off.
4. Wait to dry- which should be quick if it was a thin layer.
5. Now the stickers will be protected and mroe difficult to damage due to transformation and play or even daily handling.
Note : this method also works for paint works especially on Transformers.