Go grocery shopping. Housewares aisle. COPPER ChoreBoy pot scrubber. Wet the slide with a good light oil (I like a product called Kroil, but use what you have) Let slide marinate for a couple of hours.
Moisten the COPPER (not copper plated steel, but COPPER) pot scrubber with some oil. Rub gently. Slide will turn a coppery color.
Take a clean soft cloth, few drops of oil. Rub slide, changing to clean spot now and again. Copper color comes off.
You CAN use steel wool, bronze wool, etc etc etc- this will do the LEAST harm to your bluing.