Originally Posted by coastrider
Probably of no help, but I have seen this part in a pic before, either on this site or one of the Facebook groups. Came out on the drain plug the same. Exactly the same with a number stamped. Is definitely not a valve shim because they are much harder material than that appears to be and they are not stamped.
Thanks for the tip. I'll start scouring the forum to see if I can find who else has had to deal with this.