I have been experiencing water leakage both front and rear so severe it tripped by computer until it dried. On other forums I have read of clogged drain tubes. The crimped outlet being blamed for holding small debris.
The front drains exit below the A-pillar near the door hinges. The rear drains exit below the rear window inboard of the C-pillars. The recommendation is to clip the crimped nipple and manually clear the outlet, but the rears are inaccessible. The suggested resolution for the rear is removing the headliner and blowing from the top. Before you do, try cutting the rear crimped nipple with the paring knife used on the Thanksgiving turkey and ream the outlet with a properly bent wire hanger section.
Nothing in the service manual speaks of this system needing routine maintenance, but then again the manual is written for BA majors.