Or, for that matter, the mounting hardware itself... If the product packaging and/or the mounting is also being heat cycled, it's possible that they are "walking" too.
If you use binary resistor values, say 1K 2K 3.9K 8.1K, etc, you can then have a resistor ladder with a 1K resistor in series with your estop chain (with a resistor across each estop switch), and then use a DAC to measure the voltage, and a comparator to directly feed the e-stop state to your...
