I have an old caroma toilet thats having an issue with dripping/running having removed the lid to the cistern, I have discovered that the float doesn’t seem to rise enough to seal the fill valve and stop it running completely once full (if I live the float just slightly it shuts off). The toilet seems to be a march 1979 manufacture (took a photo of the indented writing on inside of back of cistern zoomed and discovered a 3 79 date on it) so we are talking about a 46 year old toilet, the fittings all seem to be plastic and I have in the past replaced the arm that the button hits to start the flush process. My question is does the fill valve have an o ring and could degradation of this ring be the issue, also would this be an easy diy fix to replace this or should i call on a plumber? Any info on this would be helpful thanks.