In 95 and 96, the US mafia allegedly got in touch with three Yakuza leaders : Yoshi Teriyaka (Boryokudan clan), Kasuo Taopka (Yamaguchi Gumi Clan) and Masao Ori (Sumiyoshi Kai clan) in order to develop a pornography business with them.

In 97 and 98, it is also alleged that Yakuza henchmen were involved in the Killing of Marvin Jarv, the leader of the Jamaican posse in NYC who tried to move on the Mob territory in the Bronx.

Apparently Bonanno capo Mickey Zaffarino was the main point of contact between the Mob and the Yakuza.

To be honest, this is all single source and it has never been confirmed.