1989.06.30 - L.A. Weekly - L.A. Dee Da (Slash, Duff)

Transcript (excerpt):
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WE CARE A LOT: Apparently Guns N’ Roses aren’t spending all their time while in Chicago (not, as we’d heard, Canada) doing pre-production on their next album, because not only did Slash take his mom to David Bowie’s Tin Machine show, but he and Duff joined Faith No More onstage recently at The Roxy. Slash was telling people that he hasn’t been to a show in the last six months (is it that he hasn’t been to a show — or just doesn’t remember having been to a show?), but that he just loves the Faith record. The Gun-duo joined Faith to jam on the Black Sabbath song “War Pigs,” which departs into a jam at the end anyway.

Afterward, however, Slash was lamenting to a few pals that he really didn’t know the song very well; overhearing this, a woman standing nearby jumped enthusiastically into the conversation, advising Slash that when jamming it really doesn’t matter so much whether or not you know the song, but just that you go with the flow and jam. Rather than go with the flow of this well-intentioned guitarist-bonding, Slash and his friends just looked uncomfortable, until one pal said, “Uh, c’mon, Slash — it’s time to go.” Like, who is this whack babe trying to give a superstar dude advice? Well, the babe was none other than guitar goddess Sylvia Juncosa, who got the impression that Slash isn’t exactly used to women being critical of prowess after a performance.

Tin Machine played in L.A. on June 16 and 17
https://en.wikipedia.org/wiki/Tin_Machine_Tour

and Faith No More played at the Roxy on June 19, according to this site:
http://www.fnmlive.com/1989

So this means that Slash and Duff were in Los Angeles at least between those dates and then returned to Chicago (it also seems Axl was in Chicago around those dates):

https://www.a-4-d.com/t3130p90-notes#16220