"The fabled Passage of Slerotin leads deep beneath the Hellfurnace Mountains, rumored to hold mysteries and treasure. Your group has prepared for a cautious and perhaps lengthy expedition deep under the Flannaess. The town of Dark Gate is your last stop in civilization before leaving on your sunless journey. As you approach Dark Gate, however, hyou see an ominous column of smoke reaching into the sky. And where there's smoke. An adventure for APLs 2 to 16." by Ron Lundeen (One-Round Living Greyhawk Core Adventure COR3-16 "Lerara")
The Lerara were a group of Suel who were lost near Slerotin's Passage when the Power Mage made his way through there with the survivors of the dual cataclysms.
"Brave Heroes: Our town of Dark Gate is being terrorized by forces unknown. Someone or something is kidnapping residents who step outdoors after dark. Some say the ghostly Lerara Suel are to blame,ranging out at night from Slerotin’s Passage. The Border Guard here in Dark Gate are brave, but are stymied by these attacks. If you can help us, please hurry to Dark Gate. –Spokesman Olmir. A two-round Yeomanry regional adventure for APLs 2-12." by Ron Lundeen (YEO7-07 "Dark Gate Stalkers", featuring "ENCOUNTER 5: THE PASSAGE OF SLEROTIN")
CORS4-01 "Sea of Dust" continues the action of COR3-16 on the desert side of the tunnel.
... there are also a few short references in the LGJ (pp. 64, 143, 155, & 163)
In Dragon #241 it is stated as extending from hex S5-141 to hex O5-134 of the Darlene maps. This source also states that the Lerara culture are primarily located in deep tunnels in hex Q5-137. It also quotes the following "References: #1015 WORLD OF GREYHAWK boxed set (1983,Glossography, pages 27-28, “The Lost Passage of the Suloise,” and A Guide to the World of GREYHAWK Fantasy Setting, page 8, "A Brief History of Eastern Oerik”; DRAGON Magazine issue #139, “Lords & Legends: A miscellany of magic-users,” page 18 (Elayne Mystica)."
#241 also describes in detail the lost "Slerotin's Manifesto" rumored to be in the hands of the Scarlet Brotherhood.
Possible hooks:
ADP8-03 "Expedition to the Ruins of Greyhawk" has a brief dream encounter describing the Passage (J2e), but it also more generally covers some of Slerotin's character background.
CORS3-03 "Return to the Ghost Tower of Inverness" puts the PCs in search of an Octych (a quasi-artifact created by Slerotin) and also a Soul Gem possibly containing Ontovar (one of Slerotin's apprentices).
ONW5-04 "The Truth in Music" makes a book "On the Tears of Istus" available to the PCs which supposedly details the original flight of the surviving Suel as a possible adventure hook from the village of Grindle near Sornhill in Onnwal.
Slerotin and the loss of the Lerara at the Passage is also detailed in a fresco in KEO8-02 "The Daunting Spire" which takes place in the Tower of Valadis near the Castle Draconus Imperious in the Barony of Dilwych in Keoland.
In SHE3-01 "Have Tome Will Travel" the PCs are recruited to recover several scrolls, one of which is near Dark Gate. They are given a map to follow into the Passage in order to recover the "Treatise on the Plane of Shadow" located in some side tunnels there and which (according to SHE4-07 "A Matter of Trust") belongs to one Asberdies the Lich in the Yeomanry who also has minions in the Passage.
In YEO4-02 "Petals" the Gatekeepers of Westburn are said to have cleared most of the passage of hazards and to have mapped it in detail. The map is on display in Dark Gate as part of an historical exhibit for the area.
In YEO5-01 "Attack Dogs" one Blake Whitesheaf (Male human Pal9 LG) of Daywine is said to have ended his adventuring career after sustaining heavy injuries in "Slerotin's Tunnel" so he probably knows some of the Passage by heart. The Scarlet Brotherhood is also stated by this source to have several agents in the Yeomanry searching for information about the Passage so that they can establish control over it.
RR01 "Suel Imperium: Age of Glory" (TSR, WOTC, Randy Richards, 1998) sends the PCs through "Slerotin's Tunnel" to a time portal called the Null which transports them to the Temple of the Magi in Ancient Seul before the Twin Cataclysms, there they actually can meet Slerotin, a Level 29 Wizard at the time...
see also Encyclopedia Greyhawkania 2003:
Slerotin [NPC]
WOGG - 27
Slerotin, Passage of {Tunnel}{Slerotins Passage}[STR]
LGJ#4 - 16
Return of the Eight - 60 (Theodain Eriason, a Member of the Circle of Eight - another potential guide or plot hook)
TAB - 38,55
TSB - 3,4,23,24
WOGG - 27
