Is the spring on the mag catch/release button okay? I mean, when you insert a mag, the little guide bar should go through the hole in the center of the catch part on the back of the magazine, and the little "angled" part at the bottom of that same catch portion of the mag should catch on the top (inside) part of the mag catch/release button assembly in the rifle. As long as the catch at the top of the release button assembly is there and isn't bent and the return spring is functioning, it should work. What sort of shape are the mags in? I'm guessing the mags aren't the problem though, since none of them are working. Shine a light up in where the catch piece in the rifle is and see if there's a bunch of trash in there or anything that could be keeping it from hooking up to the mag properly. Also, does the mag release button feel like it's got a decent amound of spring tension on it? Or is it just flopping around? Maybe the spring is broken or came loose? I'm just guessing here. I wish I could see it. That sure would make things easier.
Anyway, good luck figuring it out. Those are nice rifles. I've had one since the mid '70's and love it.