Cars rust. to claim newer doesn't, well, you haven't seen 20 years yet.
I found something interesting. I have been running the same models for 12 years, its an old sube.
23 years this month. I do alot of welding, I mean a freakish amount. It would take a day to decipher how much I have welded.
I found in the winter, if the battery isn't packed correctly, around the steel brackets that hold it in, and the bottom, a substance builds up. not on the posts, but on the steel brackets.
its a bit salt, and definately a metal, maybe calcium ... and it loves to appear after snow storms...and the bracket has gotten thicker. it is not the same guage as when it began.
I found anything with rivets gets very very tight and stays there, usually inspecting in the summer I find these things... something extra is building on them. Welds at 60k psi, aren't the same size glob I welded..they shrunk...
Where Is It going? How does solid steel "flow"?
The icing on the cake was finding the welding wire material, on a unpainted spot under the middle of the car. I didn't weld there, how did it get there....it perfectly filled in a small unpainted spot, shiny as the weld wire...
I concluded, it is self electroplating in nature.
by its own battery, salty maine snow storm (especially), flux in the weld wire to be a strong enough acid for the cathode anode part of the process... to linger for months and years afterward apparently.
I got a laugh out of it. I learned years ago, the welds will look like they disappeared if less than a .25 inch bead, a mechanic told me this...I never got an explanation until the internet. Underneath all the protective coatings...the steel is alive.
Newer cars have a different process, it is more towards the grade of SECC found in computers. They can take an electrical pounding for a long time (including hertz). the old cars need a bit of work...but end up a bit of something nothing else will be...
if you have mysterious electrical gremlins, this is one reason, and urethane with primers an other coats is a stopper ...its called paint.
worth a mention. I find some change grounds in thier cars, and blame them first. It really isn't the grounds, it is what the grounds are attached to, and it can affect efficiency, of course.
I just babbled all this to mention paint with real stuff. The two part urethane is the best winner yet.