Oh so it's not a helical spring, it is a flat spring. I get it. I will look tonight.
It doesn't rotate down easily. There is spring action there. It just might not be enough to keep the lever up. So my guess would be it became too flat not exerting enough pressure any more.

Tony,

Congrats on your new gun, nice to hear about its accuracy. As for the take-down lever spring, I would NOT advise you to re-arch it. It is very thin and quite brittle. Please do not ask why I know this. Make sure that the groove in the frame in which the spring sets when closed, is clean.

Good luck!

Balder

Tony;

Because you are actually a shooter I would recommend following up Marc's advice and getting a replacement spring for it. That is a key part of the gun and if that lever falls completly open (down) when a round is fired, the only thing stopping the reciever as it goes into battery is the little lip on your trigger plate. It is not meant for that and won't take the abuse.
It will be MUCH easier and cheaper to put a new spring in than to try and find/replace your trigger plate.

Gary