Not sure if i can put this question here but here goes. I have recently acquired a gas cooker which is in perfect working order. The only problem is the top of the cooker has some real bad burnt on grease (looks like theyv'e been there for quite a while). Could anyone suggest a way to get rid please? I have tried all the usual household cleaners and vinegar, bicarb, baking soda etc but to no avail.