I have the above mixer tap in the kitchen, and it is leaking water at the base of the swivel. On pulling it apart I found 2 'O' rings. These have a square outer profile and I am wondering if this is how they are meant to be or is this just the result of wear. Nowhere seems to stock 'O' rings with the square profile so I need to know if the ordinary rings will do the job. Thanks for any help.