LeatherNeck...
Take a good look at the clip latch where it holds the enbloc clip in the receiver. If that's too worn, it might have some effect.
Most likely, however is that the clip latch
spring has weakened. You can pull the clip latch pin and clip latch, stretch the spring, reassemble and test fire, and see if that stops the problem. If it does, get hold of a new spring (Fulton Armory, at
Fulton Armory: FAR-15 Stuff, Garand Stuff, and More! has a good one. No, I don't own any Fulton Armory stock, but I've used their springs!) Get their heavy-duty spring; it's worth the extra money.
(M1 parts are to be found at
M1Parts on the Fulton Armory website.
Hope this helps.
Ben Hartley