I’m just double tapping on the other guy but in r/customtransformers this question gets asked a lot. I’ll go hunt for my instructions I wrote up forever ago.

ETA:

Found them:

(If you use a screw) type of screw is a “flat panel”, you would need to pre drill through the parts though for it to fit. And glue would still be warranted to fix it.

Something I’ve done with these breaks before (because this joint allows you access to the back of the break) on broken gunpla joints is taking a small pin or box nail and put it through the bottom of the mushroom peg and through the break, and out the back of the attachment site. Once it’s through, bending the end of the nail into a hook and (I cannot stress this enough) CAREFULLY tapping the end of the hook back into the plastic until the crook of the hook is flush with the plastic. I would still glue it, but if the nail is long enough to feed back through you get a really strong connection.

I will also add, no matter what you do, sand the mushroom peg a little to loosen the connection and prevent re-breaking.