Looks like my ancient Mansfield toilet needs to have the flush valve\nseal, possibly the entire assembly replaced. Although messy doesn't\nappear to be too difficult a job.\n\nCurious as to whether that flush valve assembly could be replaced with\nsomething like a Fluidmaster? Would it be a straightforward substitution\nor are there pitfalls likely to be encountered. Are these things at all\nuniversal?\n\nAt this point in time I have not yet removed the valve so I don't know\nexactly which model it is. All I can tell now is it is mostly plastic.