The FAN & heatsink seem to be the limiting factor to a computer's life
Ummm, not really. Heatsinks don't go bad. They are just chunks of metal that sit there, and are not subject to any wear and tear, or friction.
All fan bearings WILL
eventually wear out, but fans can easily be replaced, so they do not impact the life of the computer - assuming heat is still properly managed. Also, it is actually bad to oil fan bearings. These are "sealed" bearings that use permanent grease for lubrication. Oil, also a petroleum distillate, if it gets past the seals, will break down the grease and it's protective values. So the best thing is to just keep the interior of the case clean of dust, keep an eye on your temps, and listen for an increase in fan noise and vibrations (symptoms of worn bearings).