I know this is late (hope you are still monitoring the board) it's been awhile since I been looking at the M1 Garand threads.
First off - Welcome! Saw that this was post #1 for you.
As to your trigger housing............. since you say it "goes back in easily and latches tight", I get a "dissconnect."
Try this: cut two thin strips of cardboard stock (about the thickness of a notebook cover) and put them on either side of the stock so that they are between the trigger housing and the stock. This should tighten up things and prevent your problem. A good trigger/stock fit should not go "easily" but require some effort to close. Ideally, you need some effort to close these.
If the wood in the stock is so compressed that this doesn't work, additional wood may need to be added there. As a last resort, you could buy a new stock. Please note that the "cardboard trick" will not be allowed in certain DCM competitions. It should help in the accuracy dept. though.