I can't resist this bikeshed, but you've written the Maximum Hacker News aside of the week. I have several car factory service manuals. They do not include cost benefit analyses on when to remove a vehicle from service. Instead, they are full of flow charts on how to diagnose problems. Each flow chart ends with a "If nothing failed a test, but the symptom persists, replace the entire part/assembly."

The goal is to pinpoint which piece of an assembly might have failed and only repair or replace that one piece. eg bad wiring harnesses, a single controller in a complex system such as antilock brakes, a single fuse, etc.

The decision whether to keep attempting to repair an ailing car, or stay in a role that supports a company doing "wildly illegal stuff" is beyond what tech writers can determine for you--even given thousands of pages of information in dozens of PDFs.