Deep hard core cleaning

From GEAppliances.com: Microwave - Cleaning Recommendations To minimize the possibility of electric shock, unplug the microwave from the power supply before attempting any maintenance or cleaning. Spills and spatters clean up easily with a damp, soapy paper towel or sponge. It is best to clean soil as soon as it appears. Baking soda and water may also be used. If the food has cooked onto the interior, heat one cup of water on full power for three minutes. The heat and steam help to soften the food. After the three minutes, allow five additional minutes stand time then clean as usual. A non-abrasive scrubbing pad cleaner works well for stubborn stains. You may use mild dish washing liquid or cleaners specifically listed for cleaning interiors of microwave ovens such as MicroBryte® (wx10x3030) or Microwave Oven Magic®. We do not recommend using other detergent based cleaners because they can cause the plastic parts to crack. You may purchase microwave interior cleaner by calling our parts department at 1-800-626-2002, on-line from GE Parts or from your local grocer. For stainless steel interiors of microwave/convection models, we recommend a plastic, soap-filled scouring pad. Rubbing gently with this pad will help remove soil. For the door surfaces (both interior and exterior) We recommend you use only mild, non-abrasive soaps, or detergents applied with a sponge, or soft cloth. For the control panel Wipe with a soft, damp cloth. Dry immediately with a soft cloth. Do not spray any solution directly onto the controls Important: Commercial Oven Cleaners, abrasive cleaners, or cleaners containing ammonia or bleach (can make the plastic brittle) should not be used on any part of the microwave. -- From me - Maybe local restaurants in your area would have some tips? Otherwise, try a Google search for keywords: cleaning stainless steel oven