General electrical questions

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I still use 60/40 solder without any extra flux but have used lead free and silver solder in the past at work and they work well too. I have used extra flux in the past at work, particularly on older connections and wire which helps. I do not remember what brands were used.

Cleaning connectors - try alcohol and q-tip, if it needs more use a toothbrush and alcohol. Isopropol alcohol is good and it does not have other crap in it to cause any harm to connectors or wire. It will evaporate off to leave no residue. I do pour some over the cleaned parts after brushing to remove any impurities.
Contact cleaners also work but as you said aerosols not desired in your workshop and you still may need to brush.