Well, I changed the oil in my '98 YZ400 and noticed the weep hole for the water pump spitting some anitfreeze out. So, after researching this on TT I ordered the appropriate seals and o-ring and finally got them today. I removed the pump cover, had no problems and thought "this will be a quick easy fix". The impeller showed only 10 lbs of torque per the manual, so I started easing the socket wrench to take the impeller off. I had the bike in gear and was holding the rear brake for some holding force on the water pump shaft. It gave way to the wrench and started spinning freely......not just the impeller, but the shaft too!!!!!!!!!!!!!! BUMMER. Now, I have to remove the right case cover and check out what happened. Hopefully it's just the impeller shaft... Anybody have something like this happen??