My partner snapped the key for her Toyota RAV4 last week. The key is supposed to have a small screw holding the metal shank (the internet told me that’s what it’s called) in place in the plastic body, but this has been missing for a while; eventually, the plastic shoulder snapped on one side and the shank came away altogether.
I found a replacement screw with the correct thread size (from a MacBook battery enclosure), although it was a little bit too long – so I had to use my (new!) bench grinder to shorten the screw length. Then I used two-part Epoxy Resin to seal and bond the cracks in the plastic key body.
So far, all working normally again and all in one piece ever since!