If the word "gender" serves no purpose in describing sex stereotypes, since you say feminists never even used the word (since the term 'sex stereotypes' made it redundant), then why should it matter that I use the word 'gender' to refer to sex, in order to a) better differentiate biological sex from sexual intercourse, b) speak the same language as everyone else, whether colloquial or academic?

There is a chapter in the Female Eunuch called 'Gender', & it's not on "sex stereotypes", but like the OED, Germaine Greer isn't American, so it doesn't count, I guess?

Anyway, I did a Google Scholar search, customising the range from 1919-1985, confining the search to: "gender" -transsexual -identity -masculinity -linguistics resulting in about 76,800 results, as far as I could tell, gender was not referring to grammar or sex stereotypes in the majority of cases, but biological sex instead.

I asked you whether there are any American 2nd wave feminists who make the distinction between gender & sex, defining the former as "sex stereotypes". You didn't answer the question. However, I looked up Kate Millet's Sexual Politics, bc I remembered she had a useful glossary at the end of the book. She quotes Robert Stoller directly, using his distinction between gender (masculinity & femininity) & sex (male & female). So you could have used that example, except that, she says she agrees with Stoller & Money on gender identity being the result of gendered conditioning, which might have made the example too inconvenient for you to mention, presuming you still reject the aforementioned notion. So Stoller really seems to be the originator of the distinction you're referring to. It turns out Dworkin quotes Money on gender identity too.

What? That hangup/neurosis is theirs and yours, not mine. I've never depicted biology as obscene. That's on you & the POV you're defending.

Tsk, tsk, reading comprehension issues. Sex (the word, the connotation, the definition used in the majority of cases to mean intercourse) is obscene to the mainstream, biological sex (male & female) is taboo to the trans cult. Saying "sex" in place of "gender" helps the trans cult make biological sex obscene to the general public. I'm saying this for the third time in a row now.