Thanks for posting this problem. I am having the same problem. I have to turn the water supply off under toilet and then back on before tank fills. If I just leave it after flushing, over time it will fill. I will try replacing the seal. Many thanks again.

After opening that stop valve try raising and lowering the float, does the water turn ON/OFF as it should?

Hi Bratsky and welcome to The Plumbing Page on AMHD.
You piggybacked on a 4 year old dead thread so I gave you one of your own. Before you post look in the upper left hand corner for the date..
I don't know if replacing the seal will help. The way you describe it sounds like the problem may be in the supply line. Let me explain.
If there's a small piece of trash or mineral buildup in your supply or angle stop the water will flow until the trash gets sucked up against a seat where it shuts down the flow, Turning the water off gives it a chance to drift back down until the water's turned back on. Does that sound like your case? Back to you, Tom