I took a gamble when I bought the tractor mower. It was old, but well-cared for and ran well, but it was wearing out. Still, I couldn’t get a quarter as much machine for twice the price. Two months later, the mower deck cracked, rusted out from ten years of hard use. A replacement deck would run into the thousands of dollars, there were no options for just the shell, a cheaper, but still pricey option, and there were no off-brand decks to be found. Those three facts alone should tell you that we’re dealing with a John Deere, here.
Here’s the short version: Tractors are complicated and increasingly controlled by onboard computers. These computers use proprietary software, and that software is protected by the Digital Millennium Copyright Act (DMCA). The software itself is encrypted to prevent copying or modding. Those encryption are also protected by the DMCA. Breaking that encryption is illegal, regardless of the state of the software. If you have to decrypt the software to remove it, you’re breaking the law.