My son recently bought a house, the previous owner of which did extensive renovations of the plumbing, including enclosing the WC in a Fort Knox of plywood. Water has started intermittently leaking into the pan. I have fixed a similar problem on my own WC (replaced the siamp valve) but mine has a circular pushbutton which I could unscrew by pushing the buttons down and gripping the inside. But this thing is elliptical with an elliptical chrome collar and I am not sure how to proceed. The top panel does not lift off and there are no screws to be seen. Also, is it possible to identify the flush mechanism from that eccentric oval pushbutton? Reason I ask is, if it doesn't include a siamp valve the job is probably beyond my competence.