I'm trying to fix a leaking push button flush valve as it keeps leaking into the toilet bowl & wasting water. I've had a look at the washer... it doesn't look worn and I've cleaned everything up to make sure no debris was getting in the way.The toilet is a vitra and it's concealed so I can only access from the top. Is there anything else I can try or does anybody know where to get spare washers? Screwfix, Plumbworld and B&Q don't sell them. It appears vitra don't either!