Asg .308 l96 mag problems

[LR18]

Hi,I bought a second hand asg l96 about 2 weeks ago. It's been working perfectly when I've tested it a few times in the garden but today when I took it to airsoft for the first time the mag wouldn't click in place. 

 

I asked a Marshall to look at it and when trying to figure out the issue we lost a small spring from the release latch. 

 

Any ideas what the problem could be? Also how important is that spring? 

 

Any close up pictures of a working mag mechanism for this gun would be greatly appreciated.