Wow! Thanks for taking the time for that thorough report. It gives the rest of us a great idea of possible future maintenance. Let us know when/if you end up replacing the carbon rods.
I think it would be pretty neat if from this thread, we would be able to give a general estimation of the expected service life of some of the major parts like the carbon rods, stepper motors, belts, etc. (example: from community experience, the life of the carbon rod assembly is generally xxxx-xxxx hrs)
Of course, this would be a very general estimation. Since wear on the various parts can be accelerated or slowed by variables such as average print speed, types of materials printed, and even variance in quality of materials between batches of parts. So it would not be a hard and fast rule, but it would at least give the Bambu community some anecdotal information for what to look out for as different parts wear.