Same problem with my stock also for ruger American. I was able to find a washer to fit inside outside diameters. No problemsI am sorry to hear this...while I have personally had pretty good luck with Boyd's, I lied about not having had any issues. Mine was kind of similar, but I fixed it myself. I almost forgot this even took place. I bought a stock for a Ruger American and it had a plastic latch for the magazine catch to engage. It worked, but it was retained by one of the action screws and when I tried to tighten the action screw I didn't get it very tight before it split and smashed away not allowing the action screw to ever get even close to being tight.
Rather than send it back for another piece of plastic I made one out of aluminum. It works fine and I am happy with the stock. If I had sent it back and they did me like they did the OP I would have probably been upset too.
It is disappointing that a manufacturer doesn't know better than to try and make these kinds of parts out of soft plastic. It seems like they are one of those outfits that does a heck of a lot of business and just cant bring themselves to admit they are wrong and need to fix something. I feel like in doing the repair myself I have added to the problem...they don't have a clue.