Toilet supply line leaking at toilet connection
I'm hoping that somebody sees this - I just ran into the same problem as the OP and spent some time researching &amp; investigating the issue.

The problem is that the gasket that comes on the valve is actually still inside of the toilet tank inlet - it's just lodged/displaced &amp; difficult to see. If you shove your fingernail in there you'll feel the rubber gasket.

Simply remove it (without using any harsh tools that may nick/damage the rubber), put it back on the valve, screw it back in and test again. I just did this and the spraying/leaking problem is gone.

Hoping to get a few more years out of these pieces of junk before I eventually replace them all.