I use any type of oven cleaner overnight - but prefer Dr Beckmans' Rescue. The very strong stuff you paint on with a brush is also good - but the fumes are dreadful.
Remove gunge with kitchen paper towels. Then scrub with hot soapy water and a stainless steel pan scourer - it will not scratch, and is far better than 'brillo' pads.
If you can get door off soak in a solution of areial washing powder, I do this to the bottom of my oven and it works a treat. Chefs do this to clean their ovens!!! Hope it works for you