Flip top leaking bad

My 73 /6 duster with manual disc/drum setup is dumping brake fluid from the reservoir. It's sloshing out of the top when I come to a hard stop or take corners really hard. I've bent the clip to put more pressure on the lid and it's a pain to flip it closed now but it still leaks. I even thought it was because the top opening wasn't straight so I milled it a little more straight with a file. ( don't worry, I cleaned it all before putting it back together :) )

What am I missing??