Aaaand back to the original question. I was advised by a woman who used to run a restaurant. This definitely works and is easy.
I bought one of those under the bed bin things that are flat and large. Big enough for the racks to sit flat in. You also need a packet of Lectric washing soda ( sodium carbonate). Put about 1/3 pack of washing soda in your bin thing and bucket in hot water to about 2/3 full. You will be best to do this outside, because the thing is heavy when filled and you will have to upend it to empty it later.
Put your racks and side racky things in the mix and go and do something else for a couple of hours. The water will get all brown and icky as the goo comes off. Sometimes I tip the racks over a couple of times, make sure they are submersed.
Poke at the goo on the racks when the water has cooled to lukewarm or cold, and you will see that a lot has come off and a little remains but is soft and easily moved. Take the racks in to the kitchen sink one at a time and wash in soapy water, finishing off the bits that are still stuck with the steel wool. It will come off very easily.
Dry racks, put oven back together again. Tip out the icky water and hose off the concrete.