I have a JD KBA-7-10 disk, new to me. I have used it for about 8 hours. After 8 hours one of the front disk gangs stopped turning. It turns until it encounters corn stalks or resistance and then stops turning, while debris gets pushed in a pile in front of the gang. The only zerk fittings on the disk are on the wheel cross bar and on one wheel. I can easily turn the gang by hand, as I can the other three. I found a manual online, but it does not contain a troubleshooting section. What caused the gang to not work properly and what can I do to fix it? And, should the disk gangs have grease fittings?