homer i dont use products on my microwave, find if i put a strong mix of soapy liquid and less water highly concentrate, and then put in the micro and then let it come to the boil and switch off and leave for a while the steam seems to soften the dirt and its easy to wash off then but it sounds that your micro is pretty ingrained if so dont know if this will be enough, give it a try though you may have do this several times good luck!!!
Buy a tub of household paste [Astonish brand or similar} you can buy them in the pound store, use an abrasive sponge with some paste, should work wonders, I also put my microwave plate in the dishwasher but remove the burnt on bits first.
have done the soapy water mix and put into microwave. it is only 9. am so haven't looked at yet.
My dog got out last night and whilst I left back door open for him he never came back. I drove around in my car then came back then walked and there he was trapped behind railings of pub. Anoother man and myself squeezed him through. So he is a joyous dog today - unfortunately he going to kennels this afternoon as I am going awayyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy. See you when I get back
if it's just the ceramic plate, take it out and give it a good soak in a strong solution of biological washing powder and hot water. In fact, this will shift most sorts of grime from burnt-on fat on cooker racks and baking trays to tannin marks on cups.