I think this answer has helped me. But I would like to clarify your advice.
Today, I put a bucket under the stop valve to catch the dripping water. Then I opened the stop valve all the way. The toilet bowl filled with water to about 1/2 full (probably too much, but this is just a test).
The water was pouring around the rim also, as if someone had tried to flush the toilet. Water is CONTINUOUSLY being swiriled around (just a trickle, not the full blast when someone flushes toilet). And I can hear the water going down the drain.
So I think, well, I never flushed the toilet but maybe it just needs to balance out before it can be in use. So I wait a while, and no change. Continuously trickliing out the rim, and a drainning. Water level stays pretty much the same - perhaps slowly over span of 10 minutes, water level went down 1 "
So.. no dice.
I then try the flush handle.. but absolutely NOTHING happens. No roaring flush.
I slowly close stop valve, and trickling water slowly stops. I try flush valve. Nothing happens.
I think I need to replace or fix this stop valve as you suggest. But there seems to be another problem, the water doesn't stop, and the flush action doesn't work.
Are they all related to same issue? A leaking stop valve? Fix this, and the rest gets solved magically on its own?