OUCH! My rear end hurts

[truckster]

About a week ago I noticed gear oil under my rear differential (72 Blazer 4X4). No big deal, so I parked it. I drove it down to the office and back (about 4 miles total) and parked it again, and today I noticed a lot more gear oil. I pulled off the back cover to replace the gasket, and there was a piece of metal that went partway through the cover. It's about 1/4 by 1/2 inch and less than 1/16 thick. There were more in the bottom of the housing. Any ideas what gives? All of the metal is flat, so I don't think it's a piece of the ring gear or pinion. Maybe a shim? Do I put it back together and drive it?

Also, it's supposed to be a posi, but I don't see any springs or plates. Maybe it's been replaced before - there was some silicone gasket on the inside of the cover, like maybe they plugged a hole before.

I just got the top off and I really want to drive my Blazer, but I don't want to ruin it. Any help is appreciated.