how to repair split cogs?

i know i should know this, but usually im able to scrounge up a replacement from somewhere. this time, im stuck!
the tokyo disney train i got last year never ran well, and i finally took another look at it today, to find a split gear.

the top one is the tokyo gear... the split can be seen. ive found a similar size cog on the bottom set from a vintage magnetic engine, but cant see how to fit it to the original bar, so im thinking a repair is the way to go.


ive heard of using a kind of glue, but what glue, and how do you hold the join together until it sets?

thanks in advance! the disney train and i will be greatful for any help and advice!