the top bolt would not tighten anymore (even when i losened the headset) so i decided to take it all apart clean it and put it back together again. so i took off the top bolt, took off the headset, removed 2 specers then took the fork from the frame. on the bottom of the fork (just above the ^ where the frame meets the fork) there was a little circle of metal with small balls all around it. i know very little about bike parts so i dont know wat this is. ANyway i cleaned all the thinkgs i took off and put it back together, tightened everything up but the fork still shakes. Am i missing anything that should be on the fork? what else can i try?