The leak on my HD4601 was the same as yours. If you take the lid off and look inside, opposite the spout you'll see a black plastic part with a domed top. This acts as a funnel for the steam to activate the "auto switch off". It's attached to the back of the kettle (behind the switch housing) by a metal plate with two small screws. The screws go into the lower end of the "funnel" part mentioned before. The water seal is made by a small, diamond shaped rubber plate. Unfortunately the "funnel" part isn't very strong at far as its screw attachment posts go, and one of mine (with continued use and heat?) had broken off, so the water seal was compromised (i.e. a leak).
I repaired mine by removing the "funnel" part, fixing the screw's attachment post back in the diamond shaped bottom with Araldite, and then reinforcing with more Araldite. Be warned, however, to get the "funnel" part separate from the kettle will require (1) fiddling with an Allen key inside the kettle to unscrew the funnel from the handle, (2) removing the black plastic base (2 screws), (3) unclipping the switch housing, and finally (4) unscrewing the small (2 screw) plate mentioned above.
I only went through all this effort because I prefer this type of kettle, but they don't seem to be made any longer. I've been searching on the Internet for a replacement part as my local spare shop has closed, but no luck to date. If anyone finds a place to get spares for this kettle then please let me know.
Doc, February 2011
