Having lived in the "salt belt" I found a rather amazing cause for a lot of damage to cars- Car Washes.
It seems several decades ago, car washes were required to manage their water output due to environmental requirements. I used to frequent a place in CT that proudly posted "We recycle our wash water".
Everyone was pleased and proud .... but as it turned out the water was as briny as the ocean! Cars were rusting through in several years etc etc. The wash had to finally close down due to the public protesting.
I suggest that if you do take your car to one of these car washes to carefully check the wash water. Someone on this forum posted how they use their garden hose and heavily flush all over and underneath their car at least once a month. This person also said that parking a wet car in a warm garage accelerates rust opportunities. Interesting.
FYI, most DIY car washes do not recycle their water.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)