I too have the same toilet seat that needs replaced. Porcher just told me there is NO replacement seat that can be used and they no longer make nor have stock of this toilet seat. I have a local company looking into the problem and will get back to me. For now I am going to take detailed measurements of hinge placement and length/width etc, and take a tape measure to every home imporvement store in the area. Anyone with any other suggestion would be greatly appreciated.
I have three of these beautiful babies from when I redid my bathrooms back in the early 2000s -- and one of them started to leak (would keep flowing a small amount into the bowl after filling the tank), so I did some online sleuthing and came across the parts as well as the how-to for a complete rebuild of the critical parts -- and rebuilt all three and they work like new. I am in zip code 94552 so if you need help from a licensed general contractor -- give me a call at 510-909-8813 and I can see if I can fix it for you (for a charge, of course).
https://www.youtube.com/watch?v=FlJ3UQlkEdU
First you will need to obtain the kit or parts necessary for replacement, compare your parts to your existing before doing anything, you will need your model number and if you had a picture more help could be offered. Begin by turning off the water supply to the toilet, keep a small bucket handy to catch the water, disconnect the supply line at the toilet if your are doing a complete replacement. If its only the handle again a handle kit will need to be obtained for your specific model no need to turn off water but keep in mind your exact handle or button placement. When you have the correct parts its just a matter of remove and replace and take photos of before so you can reference what goes where if you get sidetracked.
if you flush and the water continues to run into the bowl the it is the flush washer that needs repalcing
If that water shuts off and the cistern fills and then continues so that it flows down the over flow pipe into the bowl the it is the water inlet control washer that needs replacing