If you have tried to remove the impeller without removing the cover to hold the back of the shaft then you have probably round off the drive flats where it locates in the end of the balancer shaft
You need to take the clutch cover off to see whats going on with it
Yes they leak when cold when the seal needs replacement, as an early warning sign
The seal in question is number 4 in the parts diagram you posted
The drain is there to stop the water getting into the engine, by giving an easy path to escape
I do now understand the smart way of the construction; a double (redundant) seal with a leakage hole in the middle. I believe the water should normally not get out (also not with a cold engine...). If it does, than it is a indication that the 1st seal has a failure and quick repair is needed to prevent the second seal from failing and water getting into the oil / core of engine...These seals are dynamic seals, very prone to failure, specially the one on the water side (NO oil lubrication!)
I will check it, but i am very afraid that much damage has already been done. Look at the brown, baked color of the internals...!!! It shows that the water has been boiling hot or something or mixed with oil already..and the shaft likely was already disconnected.....Its not normal.
See other pic I last attached!
I am going to look for a new bike - wr450 2016..-. in the mean time :-) Was already planning to do this..,.
This one, which has never really let me down, is at the end of his life...
Will give a update when I figured out wat the cause was of the impellor disconnection (because that is really weird i think)....