I had replaced my axle bolts with Allen cap black oxide bolts. But with less than 100 miles the heads of those bolts are completely rusted. So I found zinc bolts at MaterCarr. I also mostly use stainless flat washers and lock washers since there is no real strength needed for those. I did see where one owner had used SS washers on his transmission bolts and they fell out after use. I don't see how SS washers caused that since the harness is the same as carbon steel.

Not sure is all black oxide bolts corrode like that but I'm not going to use them on any exposed locations anymore.