A bit scary, but this works--I have went to work with ovens that had many years
of crust and yuck. Take a small glass or stainless container, put a cup+ of straight ammonia in it. Place in oven and close door for 20+ hours. With a straight spatula the yuck will just scrape away. Maybe a mesh scrubbie on the racks?
Agree with Joe about the old EasyOff, was great when you are in a hurry, do not like spray stuff.
Nan