I've always used regular old Ronsonol lighter fluid. Put the bearings in a medicine bottle about half full with the lighter fluid...give them a good shake...let them soak...maybe shake a couple more times. Then I slip the bearing down on a sharpened pencil and spin it real good to get out the excess and then air dry them on a paper towel. One drop of Yellow Rocket Fuel and back in the reel. I have some old Curado reels that are going on 10 years old and still cast like new.
Just need something to break down the gunk from old oil and grime. Lighter fluid works really well....spin them out and one drop of oil as said above.
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I'm not sure if its as good since I haven't used an ultrasonic cleaner, but I use lighter fluid in a small tupperware. Put the lid on top, and then turn on an electric razor and let it sit on the lid. Creates a nice vibration to the tupperware that cleans then pretty well to my standards.