Somehow I managed to lose the short rack ear for a CRS112. Now it's "hanging" in the rack on only the long ear, showcasing a bad case of the physics of leverage.

I've looked for replacements but it's not even that easy. MikroTik only sells RB4011 ears as "official" replacements parts. I guess these generic ones here for Cisco might work though:
What would you say, should I buy some of those? Still >5€ for a pair, but oh well

Unfortunately, there is no option to order such parts from MikroTik.
You may try to contact your local MikroTik distributors and ask whether they do offer such parts.
https://mikrotik.com/buy