In May, BBC News revealed the site was failing to prevent under-18s from selling and appearing in explicit videos, despite it being illegal for children to do so. At the time, OnlyFans said attempts to use the site fraudulently were "rare".
Now, the leaked documents show accounts are not automatically shut down if they break the site's terms of service.
Moderators have also told BBC news they have found prostitution services advertised, bestiality and material one moderator believed to be incest.
One mod has viewed up to 2,000 photos and videos looking for content prohibited by the site. He uses lists of keywords to search within bios, posts and private messages between creators and their subscribers.
He says he has found illegal and extreme content in videos - including bestiality involving dogs and the use of spy cams, guns, knives and drugs. Some material is not actively searched for by moderators as frequently as he believes it should be, says Christof, despite being banned under the platform's terms of service.
On multiple occasions, he says, OnlyFans told him he over-moderated, particularly in relation to videos showing sex in public and to "third-party" content - material featuring people not registered with OnlyFans.
One of the documents we obtained detailing moderation guidelines in 2020, states that adverts for sex are an issue for the site. It says the "most popular places for escort promo" on the site are in creators' usernames, bios, content descriptions and "tips menus" which advertise customised videos. The document says "examples" of this promotion include references to "PPM (pay per meet)", "CashMeets", "Book me", "IRL Meet", "scort" and others.
Despite this, BBC News was able to find more than 30 active accounts using those keywords in bios, profiles and posts, on one day.
Only two of the accounts we found had been removed 10 days later.