Ok, I am having this same problem on my 2000 WR400. I pulled the push rods and checked everything out and did not find a bearing. The push rods seem too short as is to make contact with the pressure plates. Is there a ball bearing somewhere in the engine? I did not notice one come out when I drained the oil, but the bike was on the kick stand at the time on an angle. Should I be worried about a ball floating around in there? I plan on picking up a nut as mentioned above to use as a shim. Any comments?