If we're talking about things I use regularly, probably my desktop computer. I bought it at an auction. This was in '04 and have been upgrading it one piece at a time ever since. I'm currently gathering parts for another "gut it and start over" level rebuild and I think the only original parts at this point are the case and the floppy drive.

If it's just things I own and don't use, I do technically own a '76 Chevy pickup that is almost infinitely repairable but that hasn't had an engine since the early 2000s