Penn 704z Main Gear

I have a few of these hiding in my collection of old stock Penn Fishing Reel parts. I was wondering how often most fishermen or women replace these on their Penn 704 Penn 704z Penn 706 Penn 706z and other Penn Spinfisher fishing reels. I have replaced main gears due to stripping and advanced stages of corrosion. Feel free to comment on how often and why you replaced your main gear on your Penn Reel.