I decided to take one of these apart to see if I could grease them. I drill a small hole through the cap so I can pry the cap off. Inside there is a plastic ring that you can pull out, with the ring out you can clean the bearings and flush the old grease out. I was surprised to see how many bearings there was. Once clean, I repack the bearings, install the ring and cap. The cap is a freeze plug I got from the auto parts, it's a 15/16 plug once installed, I smack it with a hammer and a flat pin in the middle to make it spread, it looks like it's nice and tight and turns smooth like new.