A while back I noticed a bit of bubbling around the factory beading of the seam on my doors. As I grounded the beading down I was surprised to see corrosion on all the factory sealed seams yet no visible corrision. I eventually removed all the factory beading at the seams of the doors and had a local shop treat and redo them all. To this day so far so good.
'05 GMC Sierra SLT Z71 CCSB 4x4
'02 Regal LS
'00 740i Sport