This no way about it. Have to hack the tiles and change the stopcock.

Happen to my unit also.

What does open it back to maximum open do?

Damn dude, your suggestion maybe just saved me a few hundred bucks.

I opened to the maximum (stopped applying force once I hit the resistance)...and voila, no more leaking!

But then to be sure, I flushed and stuck around for a few minutes.

Now here's what I found. Every 12 to 13 seconds, there is exactly one drop of water leaking out.

Is this something to be concerned about? If it's just one drop of water every 12 to 13 secs, I can't be sure if I would have noticed before or not...it doesn't leave any puddle.

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According to Google, 1 drop of water is 0.05ml. If there are 5 drops in a minute, that means there are 216,000 drops of water in a month, equivalent to around 10.8l. From a cost perspective, I think it's negligible if that much water leaks from the stopcock. But is it damaging anything?

Would playing around by opening/closing worsen the situation?

Similarly, would applying a bit more force cause anything to break or become worse?

Okay I just got home again and checked the leaking now.

I measured with my phone, 5 leaks interval. The interval for each drop of water to leak out is now around 1min 10s to 1min 15s consistently. The leak is forming very, very slowly. Earlier this evening, it was 12s for each water drop to drop out. Even when the water drops out, it moves very slowly, seems like the droplet size might also be slightly smaller than earlier this evening. In the evening, as soon as one droplet falls down, I can see another forming. But now, I have to wait around 30s before I can see the next droplet forming.

I've not playing around with the tap head, nor tightened it for now yet.

Is this a good sign?

I did this (tightened it just a tiny bit) last night before sleeping, and it made things worse. Then I went back to your previous post:
I turned back clockwise a bit (loosened it slightly), and voila, I found the sweet spot. No more leaks. To be sure, I waited until today morning. Toilet is back to being done dry, no reflective sign of water anywhere on the tiles and grout. I sat there for 5 minutes just to make sure there is no slow-forming droplet leaking out - there is none!

So problem solved!

PS: Screw the bloody technician for playing with the stopcock and then refusing to come back to my unit to right the issue.