My guess is on the tailgate it is oil, not rust that is making those spots. Could simply be a leak where the spray makes it to the back of the car. Do you have a transmission pan leaking?

I had a father-in-law who sprayed his trucks (lived close to the ocean) every year with diesel.

Carefully take a close look at all areas of the car. Sometimes it simply isn't worth it chase some rust.

A quick and simple way to slow it all down is to wash the car with warm water, dry completely and then spray areas with WD40.

Don't go to car washes where they proudly claim to recycle their water, especially in the winter. You are getting salt baths each time you do.

Haasman

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'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)