This is the problem with underseal
 

Car blogger reveals how water can get trapped in vehicles | Daily Mail Online

Underseal masks the rubber water evacuation bungs which should be removed periodically, say every year, to release trapped water in the sills and frame/chassis rails. Thankfully on D2's there are only the sills to worry about but flaking rust can block the frame/chassis rail water release holes causing the frame to rust from the inside out. The worst condition is obviously the monocoque chassis on modern cars after they have been undersealed.

That is more apt to happen after leaving the factory when the vehicle have been treated by typical shyster dealers or other dumb ass undercoaters.

Normal dust, small road debris and tree dropping can cause the drainage blockages if normal drain clearing is not complied with.

If you don't care for your plumbing you might get hosed.
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X1 ............ ya gotta keep ya holes clear or ya can get a build up :laugh: