Stubborn bus bar

impact drivers are a god send for stuff like this

A, You can brighten them up with aluminum polish but the only mechanical areas of consideration for conductivity are the bottom of the lug hole and the bottom of the set screw.
A. If the bus bar will be located in an environment prone to oxidation (seashore), I would use an antioxidant compound. The Noalox compound seems to fit the bill. I know Mex has his own favorite but have forgotten the brand name. I've been using Caig Deoxit Gold spray and for less severe environments, it works well.

I seem to run into these issues at times and it usually involves the plating of the parts. I guess the thought is that corrosion is easy to spot and interference from plating is a minor inconvenience. I'd like to put a screwdriver in the hands of these guys and have them work on these parts when contorted in a close space.

Good luck with the bus bars, they should work well now that you have them loosened.

Round 2:
Penetrant: 1, Bus Bar: 0.

Heating in the oven at 500F and quenching - loosened one screw, then had to stop the experiment because smoke alarm went off. Never use oven at more than 350, so at 500 it did some "self-cleaning" :)

Picked the most expensive penetrant that was in store - PB Blaster. Sprayed, washed, and with a lot of grunting loosened last 5 screws.

Here is how the bus looks without insulators:

Mine of course is not as shiny now.
Q: After heating the aluminum has darkened. Does this affect surface contact, do I need to clean it?

Q: Corrosion was under the button-heads - I could see whitish traces around the heads perimeter. This wouldn't have happened if they didn't drive it all the way up to the hilt (just like on the photo). Screws with wires will stick out a little, and I will make sure to leave inactive screws slightly out.
BUT... If it corroded in warehouse, I wonder how it will fare on Mexican shores. Should I replace screws with stainless? (have doubts that current ones are SS). Or - brass screws? Or use a conductive grease like Noalox?

I like these bars and would like to keep them. They are small and fit well in a small breaker box that I bought.

Almot wrote:
Bars are aluminum. Screws - not sure, the color is like aluminum.

Yes, insulators are removable. How much heat?

I typically use a butane torch set. I would suppose that you could use a frying pan, for that matter.
If the metals are dissimilar, a quick quench after heating will bust them loose. Different metals have different heating and cooling transfer states so any rust or intermediate material liked flaked plating will loosen when heated and quenched.

Bars are aluminum. Screws - not sure, the color is like aluminum.

Yes, insulators are removable. How much heat?

Try using some heat. Like a small Torch or in the oven to expand metal.

Corroded in place or plating is fused to the threads. I would try soaking them in a penetrant and that would not be WD-40.
Heat will also work to free them but you should remove the insulators (if possible).