[shuntress]

That calculation is definitely an important consideration but "reparability" does not have to mean "keep an outdated machine running indefinitely".

Reparability includes design that enables troubleshooting.

For example: Run the "$x to fix versus $x+$y" on a non-functional fridge. A fridge designed for repair might have a thumb-screw panel for access to the logic board with clearly labeled test pads for fuse continuity. This (or other, similar repair-friendly designs) would allow you to more easily determine the value of "x" and more accurately assess whether "x" is small enough to make repair the more viable option.