For my mods, i usually just use q-tip soaked in 91% isopropyl alcohol for the contact pins. When you go to cvs, you'll find 71% and 91%. Just make sure to get the 91%.
If you find that your contact pins are starting to patina or tarnish, have you ever heard of a strop? It's basically a piece of leather that you use to polish an edge on a knife or a razor. Well, you can use an old leather belt (on the unfinished/undyed side) or an actual strop, just run the contact pin's ends up and down the strop a few times. It will come out shinier than brand new. Just note: if your contact pins are plated, stropping will eventually wear off the plating. Though if your pins are plated, they won't tarnish anyway

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For the rest of the
mod, I'll just rinse and wash with dish detergent when it feels grimy. It's mechanical, so no chips and boards to worry about.