..... and, after my last post on using ammonia, I found this and it has to be worth a try ............
An {Almost} Effortless Way To Clean Your Oven Racks - One Good Thing by Jillee ,,,,, scroll down, you do not have to enter your email address.
It's a description of using dryer sheets, leaving to soak, and just wiping off the racks after about 18 hours soaking. It has to be worth a try!