Your iMac could be covered under an Apple 'recall' repair:
https://www.macworld.com/article/3145797/macs/apple-will-refund-you-for-your-imac-hinge-repair-costs.html
According to a new internal service document, Apple will be offering refunds to customers who paid to repair or replace a faulty iMac hinge. In the service document, Apple admits that some 27-inch iMac models shipped between December 2012 and July 2014 may have been affected by an issue with the display hinge. It would not be able to support the weight of the screen, making it impossible to adjust because it just kept tilting forward. Apple sent the internal service document to Apple Authorized Service Providers, and it was then obtained by MacRumors.
The issue stems from Apple using plastic washers in the spring mechanism, which are not strong enough to support the weight of the display. Many customers affected by this issue have reported hearing a crack or a pop sound before the hinge stopped working, which can be attributed to the plastic washers breaking.
According to MacRumors, Apple will replace the weak spring mechanism on all eligible iMac models for free, regardless of warranty coverage. Just last September, Apple extended its hinge repair warranty program to cover 2012 and 2013 iMac models for five years, up from the original three-year period.
The impact on you: If your 27-inch iMac faced this issue and you paid for a replacement or repair, you may be eligible for a refund. You can contact Apple by phone or online to initiate the refund process.
In addition, if your iMac hinge is currently broken, you can get it replaced free of charge, regardless of your warranty. Start by booking an appointment with the Genius Bar at an Apple Store or by visiting an Apple Authorized Service Provider.