Originally Posted by Artmasterx
Certainly a valid point (The time metric is much harder to define), and I didn't intend for this to spur preemptive replacement. But it is good to understand when that it actually represents a reasonably high probability of failure. I added your quote to the OP...
Thanks for the effort to run the equations; it's a good first start.
I think time is actually easy to define. All BMWs have an "in-service" date, which the customer who bought new knows (it's the day he picked up his new car), bought-used owners can find out from BMW. Most people also know what type of traffic they usually encounter. It's another set of data that would help determine statistical failure rates.