The shaft, to get to the treasury, is in his quarters, as best I recall. There is a slot/tub you place the deposit slips in, then in the niche in the wall behind (or to the side), the doors open to reveal (what is now) your treasure.Yes, that sounds like the right spot for Al-sedexus' temple. YOu need to teleport from the rift, using the other portal (where there are two sitting at 90 degrees to each other. Follow that path and find the beckoning stone. That will open the large doors, leading to Al-sexy.
The flame vault? You mean the dome with fire all around? Yeah, that is where the staff of ash is. You need the ... something or other ... I was gonna say winterwand, but knew that was wrong. It is the flamequencher wand, the one that looks like a key. You pick that up in the rift, way before teleporting to the courtyard area.
Tools for Wizardry(r) 7