They've got those brown spots/splashes on them now that back-in-the-day we'd have used a scourer on. I know for a fact, just washing up liquid isn't going to get the spots off. But I'm also pretty sure something like Lakeland's oven cleaner will take the bright shine off. Any ideas? Also what's the best thing to use to clean the heavy duty metal grates? (It's a Britannia range cooker)