We used SuperMicro servers and their TCO increased substantially after an average of 36 months. Keep in mind there are environmental issues such as CRAC failure

We used SuperMicro servers and their TCO increased substantially after an average of 36 months. Keep in mind there are environmental issues such as CRAC failures, power stability, back EMF, etc which all harm components. It's very difficult to quantify the server lifetime, you need to be conservative in financial planning and that ended up with a median lifetime of 36MO. You can get deeper into the weeds and look at Zinc Whiskers and such but that's a niche you just have to generalize.