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Paz de la Huerta, who's already accused Harvey Weinstein of rape, claims to have new explosive facts about him, but she's willing to keep it out of the courts -- IF he ponies up big time.

According to a demand letter obtained by TMZ ... the actress wants at least $2 million from the disgraced Hollywood producer or she'll file a new lawsuit against him. She's previously sued him over 2 alleged incidents in 2010.

To add some extra firepower, Paz is threatening more damaging allegations against Weinstein. Among them ... she claims Weinstein developed an "immoral and unwholesome interest in her sexually" when she was just 14, and working on the film, "The Cider House Rules."

The actress also alleges The Weinstein Company rented apartments in NYC that were used "exclusively for the illicit sexual activities of Harvey Weinstein" ... including a unit on the same floor of the building where she lived as a child.

She alleges this rental was used to track her as she grew and continued to offer her work ... and then he raped her when she came of age.

Even worse, de le Huerta suggests Weinstein's company -- including his brother, Robert -- knew about his proclivities and should have warned her.

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As we reported ... Paz and her lawyer met with prosecutors last month, but so far the Manhattan D.A. has declined to criminally prosecute Weinstein over her allegations.

If she gets the multi-million-dollar settlement she wants, she promises not to file a new civil suit and to stop pushing for criminal charges.