100 pound propane tank Valve

I have a 100 pound propane tank that is 3/4 to full and I noticed that when I turn the valve it starts to leak I was just wondering if you can buy a new valve or if the propane company can just buy the propane from me or what.:-/

Doesw it still leak when you back seat the valve?

Yes, just keep turning it until it back seats itself.

$20 at mylocal fill station

'back seat the valve'

I think this means to undo the valve completely, so the back edge of the valve seats on the surface above it, then it stops leaking.

My water mains street valve does this too, I have wondered about it before.