Ordered replacement. The hard part was figuring the exact part to purchase. There were several somewhat different shelves with the same key letter in the exploded parts diagram. The shelf didn’t seem exactly to match any, based on the graph-paper part description. So I measured about three times and ordered the one that seemed closest.
It was the one! Three minutes to empty the old shelf, pop it out of the door, remove the mat, pop the new one in, and replace the mat and items.