I just restored 50 pieces of Super O last December. I used a quart of Evapo-Rust and a quart Quart of 91% isopropyl alcohol in an assembly line process. I bought two elongated plastic tubs at the dollar store and filled each with the liquids. Then I submerged 4 to 6 pieces of track in the Evapo-Rust for half a day, turning them over every now and then. After the Evapo-Rust I put them in the IPA to rinse them while the next batch of pieces sat in the Evapo-Rust. Evapo-Rust specifies a water rinse afterward. But after watching tinplate rust before my eyes after a cleaning and water rinse, I used the IPA to rinse the track to avoid re-rusting while drying. When finished, I ran the used Evapo-Rust through a coffee filter and funnel back into it's bottle. There's really not a lot of rust to use up the Evapo-Rust chemical and I've used it on other rusted parts since. Still have about a pint and a half.
While in the Evapo-Rust bath, I used some small dental brushes to clean inside the ends of the receiving outer rails. It was evident rust was in there from the color of the gunk that came out with the dental brushes. I used a small brass brush to pre-clean especially rusted areas before and during the Evapo-Rust bath. I used the brush to burnish the outer rail pins and the ends of the center copper rail.
The Evapo-Rust will not clean the copper center rail of tarnish. To me, this was desirable as I didn't want a bright center rail. And cleaning the inside of the outer rails really worked as all 50 pieces were in a single loop with only one lock-on powered including 6 isolated rail Super O track straights. There were no other power drops and the entire loop seemed to have a good electrical connection all around. See This Video
I ordered the Evapo-Rust from Home Depot for delivery to the store. And the IPA came from Walmart. Total ~$15 for both. I have a commercial source for reproduction outer rail pins and center rail clips if you need them. Much better than the offers I saw on eBay. Let me know and I'll post the link. Also, I have bought a dozen reproduction center rail clips at a local train show for $5 as well.