A319 Captain reports foul odor emanating from the conditioned air with the APU supplying the packs. Crew began experiencing symptoms of exposure and the aircraft was taken out of service.

Narrative

While aircraft parked at gate with crew on board and APU running and supplying packs a foul odor was detected by entire crew. Maintenance was called out and confirmed problem was with APU/PACK discharge. Smell was similar to wet dog/old socks. Almost immediately entire crew started experiencing symptoms of exposure. Dry throat; headache; burning sensation in eyes; and dizziness. Each crewmember experienced at least one of these symptoms but most had multiple abnormalities. After approximately 2 hours off aircraft symptoms gradually improved. Aircraft was taken to hangar. Preliminary evidence pointed to APU oil in conditioned air - per maintenance. Maintenance related anecdotal conjectures about the farming out of overhaul of certain components and the changed policy of replacing seals on condition rather than at specified intervals. I do not know any of this for fact; but am just relating what maintenance. said. This is at least the third such incidence of this sort I have heard about in the last few weeks. It seems to be one of those cases where components are starting to fail due to time/cycles at around the same time.