I've had a silicon oven liner in for about year but the sides of the oven are a little spotted so I decided this cold morning would be a good time to use the self-clean feature. When I took up the oven liner, there is a large black area under it (around 12 x 14"). I don't use the oven a lot, so I didn't realise there would be a build up under the oven liner. I can scrape up parts, but the rest is stuck solid. I'm concerned about using the self-clean feature with this build up in the oven. I don't think I can use standard oven cleaner as that is not supposed to be used on self-clean surfaces. I tried Totally Awesome cleaner full strength and a plastic scrubby but that took up very little. So what do I use to get the majority of this gunk up? It is not thick. The bit I've been able to scrape up is thinner than paper. But it is stuck fast.