I had my car for over a year, that I bought used, and never saw any wear on the pins. You are going to wear out the outdrives before the pins.
Unless ash you’re running mod or 17.5 2-3 times a week, I highly doubt you’ll ever replace these. You’ll probably cause more damage to the axle while attempting to replace it than it’s worth. Just get new axles if you feel they need to be replaced
Edit. Just realized you said rear... are you not running the shoes on the pins??? You know the C shaped plastic parts that go over the pins that slide inside the outdrives? If not you need to get those.
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