The accepted mode of getting otherwise unobtainable information is to go visit the cranky old hermit living in the mountains. It's just the sensible thing to do. So, naturally, everyone takes their monthly excursion to the hermit's hovel to consult him on everything, from lock-jaw to lovesickness, necromancers to nasal viruses.
Now, if everyone's always visiting the poor old hermit, there's going to be an enormous queue... "Wellcome to the Hermitt's Hovele, Please Take Ye a Number and Have Ye a Seate" reads the sign outside the packed dwelling.
Imagine the poor hermit, having retreated into the mountains to escape this precise situation...
Herbalist in the group mistakes one plant for another and mistakenly poisons the group. Not to death, but pretty darn ill with recurring symptoms until the cause and cure are realized. (Local people may be able to help rather easily. "You ate Dragon's Rot you fool, looks and smells just like mint except it has these small thistles on the root. Only grow in the Hornwood Forest, that must be where ya got them. Eat this and you will feel better in 4 hours."