Thanks for two good ideas. I'll check out the glazing putty, which I'm not familiar with. For some reason I've never been fond of plastic wood, but it could work here. Unfortunately, the shelves on SolidSteel racks only go one way, and the chip is on the front top.
I don't have access to a drill press, and I woulnd't dare redrill them without one. If the holes are not identical in depth, and straight, the shelf won't ever be level and solidly supported. If I can't get a goodlooking repair I might have to go this route.