Chosen Solution
I have a mid 2012 MacBook Pro 13” Unibody, Late 2012 Mac mini, and a 27” Thunderbolt Display and they all smell bad. They all come from different places and they smell this way right out of the box so it isn’t something that is in my house. All of them have been disassembled and cleaned thoroughly but still smell. It gets worse with heat and it almost smells like melting crayons and gives me a headaches if I smell it for too long. Is there anything I can do about this or do I just have to deal with. The Mac mini has been running for about 6 months straight excluding power outages and updates and still smell just as bad as the day I got it. The Display was manufactured in 2016 according to a serial decoder, Mac mini was manufactured in 2014 according to coconutbattery and the MacBook Pro was manufactured in 2013 according to coconutbattery.
Sounds like decomposing plastic/rubber. Over time the ozone in the air breaks down some plastic and rubber. Not much you can do to stop it, if you can identify the part you might be able to replace it. As an example Apple had a rubber sheet glued to the bottom cover which when heated makes a smell as you described
