Attached is a PDF of the magazine release for the M52. I tried to get a picture of the small spring that powers it, but the only way would be to completely disassemble the magazine release and then it wouldn't show how it fits.
With the tight tolerances inside the magazine well and the magazine release, my best guess is there is some crud in yours that needs to be flushed out. If it was my rifle, I would remove the rifle from the stock and then try soaking the area between the magazine release and the magazine well with penetrating oil and blowing out with compressed air.
If that doesn't work, then the spring is probably missing/damaged.
I hope this helps,
John K