The following quest seems to be missing:
http://www.uesp.net/wiki/Morrowind:Murder_Rimintil
It's one of the non-clan related vampire quests. It's supposed to be given after talking with Raven Omayn when the player is a vampire. But the topic just doesn't show up. It could have something to do with Raven's location, she's supposed to be in the main chamber for the mouth but for some reason she & most of the other mouths end up in the little temple in the basement by just before the hermitage. Raven's other quests work fine from there though.
They do go to the main
They do go to the main chamber... sometimes. It's a result of over-inventive AI packages that sometimes are just annoying (and sometimes hilarious - it's always weird to hear Ajira's "what can I do for good friend?" from behind her summoned Daedric helmet - that's supposed to be her training in Conjuration).
Dunno about the quest, though.