Maybe it had a defect. I few years ago I replaced a Marelon thru hull because I was replacing the Marelon seacock with a flanged one. I had to chisel off the mushroom and drill out the remainder. It was an original 1985 fitting. Back then they were a milky white, not the same appearance as the current ones. Did that about five years ago so 25 years in service and I thought it was as good as new.

Original boat builder used seacocks without flanges. Not sure they made flanged ones back then. I've replaced a few in areas I though vulnerable to damage but the majority are still original.