Well that doesn't fill me with hope.
Our old friend Victor fabricated a couple of testers for me, which I've installed. They appear to be plastic, and more or less to spec. It runs, but it's cogging a bit, so something is still off.
I'm concerned that it might be slight variation in the diameter (6 mm vs the 5.98mm that Ron measured).
I'm going to try loosening the keeper plate under the main drive gear and see if that helps.
Lee