If your Autostop valve is constructed out of aluminum , remove it from
the tank and toss it.

It's a non rebuildable unit.

If it's made out of any other ferrous metal, it can be rebuilt by
Manchester, but at a ridiculous cost of $79.00 plus shipping.

You can replace the autostop junk unit with a manual valve for about
$40.00.

And it's a longer lasting, either on or off, no frills valve.