At this point I've memorized where all of the weird little ingredients are in Finklestein's lab, but now that I've started reading Flame Shock, a Shaman blog, I realize how silly I've been. I don't use a lot of mods, so I never think to look for mods for very small, very specific things like a single quest, but it turns out I really should have, just like when most everyone was using Ogri'Lazy and I was still typing "blue red red red green red yellow" in /say to myself.
The blogger behind Flame Shock lists two different addons that are worth checking out for this quest: EasySerum and a much less elegantly named "Finklestein daily serum quest helper." Flame Shock has pictures of both in action, with EasySerum listing the location of the item you need in your chatbox and the second mod putting a dot on your minimap, showing the item's location visually. Your days of needing to start the quest because you ran to the wrong side? Over!