Yes, stainless steel will discolor somewhat. If you plan to pass the truck on to your great-grandchildren, they might have to think about doing a little polishing on the cylinder surfaces when they rebuild the brakes. Before then, I don't think it will be much of a concern. We ran dozens of miles of 4" stainless steel thinwall pipe when I was working for Gallo Winery in the late 1970's, and I'll bet the majority of it is still there, with a bare minimum of corrosion.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!