I recently overheated my 99 yz400. For ahwile I could hear the water pump knocking rythmatically, but that went away after running more coolant through it. My problem now seems to be associated---coolant leaks out the bottom of the waterpump through an overflow hole? pressure hole? Now the bike will not retain coolant it leaks out that hole as soon as I run the bike a little. Is there a seal in there or something? The bike is not running hot anymore. Can I just plug that hole for ahile?