To all of you who struggle with getting those nasty yellow marks off your seat....
I have tried everything - Bleach, T-Cut, Magic Stuff, Jif, etc etc
Today, after deciding I will be buying a new seat as can't stand it any longer, I took it off the toilet and out into the garden. I had a bowl of warm water, some toothpaste, a green scourer, a magic thing and some limescale general cleaner. I had never used the scourer before as I didn't want to ruin it!
Well, with all the stuff above and plenty of elbow grease, my seat looks brand new!!!
I think the key is, I could really put some some hard pressure on it, as I was on my hands and knees scrubbing.