I've used oxalic acid for small areas, just with a different means of application. On brake cable brazons I've taken bits of cloth soaked in oxalic acid and threaded them through the brazons. For lugs--in my case chromed lugs--I've wrapped them in cloth soaked in oxalic acid. I've also applied oxalic acid to small areas using a Q-tip, repeating the application after 10-15 minutes.

stan