Though Difficult to find, there are alot of references that state that Cisco Circuit cards are designed for at least 100,000 hrs (11+ years) MTBF and some higher end stuff up to 200,000 hrs (22+ years).
In today's networking world, MTBF is almost unneccesary in calculating support/maintenance. The Cisco EOS/EOL Program kinda affirms that.
Unless of course, the device is in a vehicle being launched toward Jupiter.
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