Don't use tantalum or electrolytic capacitors, lead-free solder, BGA-packaged ICs, exposed (non-stainless) steel, paper, or plastic, and most problems are mitigated by design. And use good halogen- and bromine-free fiberglass PCBs. There isn't anything to wear out or replace in such a properly-designed machine of modern design and manufacturing. If manufactured correctly, boards can be entirely encapsulated under an inert, dry atmosphere such that there won't be any moisture or oxygen to attack components over time. Basically, it would be able to last physically for centuries. The main sources of fragility would be the power supply and the permanent storage device such as an SSD or HDD. The former is generic enough to be trivial to retrofit. The latter could use SLC, RS/Turbo coding, and write minimization and buffering to extend the life beyond ordinary expected lifecycle.