A bigger issue I'm seeing is ordinary corrosion at metal-plastic interfaces where the magic coatings which keep the rust at bay get worn through due to vibration and dissimilar thermal coefficients. Another such problem sometimes occur when windows are not mounted with enough of a gap between the glass and the surrounding metal, again leading to the coating being worn through due to vibration and such. Look for the former problem at wheel wells, the latter at the bottom edge of rear windows.