plastic found in bottom of oil pan

[Bill Mc]

hi - i pulled off the oil pan ('91 with maybe 225k on it) to do the rod bearings and found what you see below. Several pieces of black plastic in the sump. Some of the pieces are thin and just crumble. The second photo shows the scale and some of the pieces once I cleaned them up. You can see an obvious corner with a mold mark. Any ideas on what this could be remnants of?

 

[AREA 91]

Cam chain tensioners. I would pull the valve covers and inspect them.