"Heard about" in this case refers to reading the letters exchanged between Mr. Olin and at least one customer that appeared on the model 21 board several years past, when old John fessed up to the problem.
Reading the actual letters would cause readers to understand it was the forend lug being discussed by old John. I've handled at least three guns that needed the repair, which, for as long as I've been shooting here on planet earth, cost more than $32.
$32 bought some nice guns in the era of the 1930s, when the problem surfaced. I'm sure Olin and company figured it out, and later guns don't suffer the problem to the degree the first guns did.
But, the problem exists, and can be documented.
Best,
Ted