I designed a lot of electronics for the military that always had "no dissimilar materials requirements", but we had Aluminium, Copper, and stainless steel in all of them. The Aluminum directly touched the ss.
Galvanic series - Wikipedia, the free encyclopedia
In the galvanic series [remember from 8th grade shop?] SS is high, Copper is in the middle, and Aluminium is low.
That means the Aluminium will be the sacrificial anode for steel, like the sacrificial anode of Aluminium in a hot water tank that protects the steel tank.
We only had trouble with electronics qualification in the "salt bath test" or "salt fog test" for electronics.
I have repaired enough of my own outboard motors that have bad water pumps that have been is salt water and not flushed. The failure is the pump, but replacing it once meant getting stainless steel fasteners to unscrew from Aluminum castings. They would snap off rather than come out. Newer outboards have stainless inserts so they can be serviced easier.
What does it all mean?
The big problem with dissimilar metals is around salt water and it does not make things unscrew, not even with outboard motor vibration, it makes them get stuck.
I have done calculations of what it would take to get a rifle barrel to shake loose, and I think I know why the Mausers and early Mosin Nagants had inner C rings that are so hard to manufacture. I think I know why the Rem 700 rifles I take the barrels off have goop in the threads. Rifles are right at the threshold of having the barrels fall off with simple receivers like a Rem700 or Sav 110. That may mean tightening the threads or putting in Loctite.