The post war armatures are built with a felt pad between the commutator and the windings. Liquid cleaners tend to carry carbon loaded cleaning solution into this pad where the liquid evaporates leaving the conductive carbon in the felt pad. A better method might be to clean the armature with a dry, soft, clean rag. If the commutator is still oily, spray the cleaner on the rag and wipe it clean. I then use a flat block of steel with a 1/8" hole in it with a piece of 400 grit garnet paper with a 1/8" hole in it to sand the commutator clean, smooth and flat. I put the upper armature shaft through the hole in the garnet paper and then into the hole in the steel block. Than rotate the armature which sands the commutator. This method keeps the sanding marks concentric with the brush track. After the sanding operation wipe the armature clean again with a dry rag and blow it off with low pressure air. The commutator slots are cleaned with tooth picks prior to sanding. If the felt pad looks to be so oil and carbon saturated that cleaning is hopeless, I remove the commutator and install a new felt pad.
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