I had a problem with a JD planter many years ago, and I went to the shop section of the local JD dealer, and asked around until I found someone that could address my problem. I know times were different then as opposed to now, but that might be an option.
Also, check to see if the side you're having trouble with matches the other side as far as the gearbox is concerned. It's possible that it's different, and the blades attached differently.
