I recently purchased a 1999 yz 400. The previous owner was very good about maint. and care. He told me that he recently had the water pump updated to a 426 one. He said that the 4oo's had a common problem with leaking. So after the first ride I noticed I was leaking coolant out of the weap hole. It only drips when idleing but at speeds it pisses it out. I replaced the two oil seals and the impellar shaft taking great care while installing new seals. This dis not cure the problem. (all the old parts looked to be in good cond. except for a little wear on shaft)I have spoken with some local techs. but they could not offer much advise. Is this a common problem with yz 400's? I have always owned two strokes and have been away from riding dirt for about three years so I am kind of out of the loop. Any help or suggestions would be greatlt appreciated.