In desperation, I used a fine Scotch Biight pad with Zep Fast 505 from Walmart, very carefully, because the pads are abrasive. My pad was blue Sorbathane that had turned milky white.
What ever you use test it on the bottom first. My 40 year old Platter Matter looks like new. Zep Fast 505 is a strong cleaner so don't use it on fine finishes. Rinse it well with hot waser, finished by cold, do not soak in 505 or water, for long periods because some materials absorb water. I dry mine in the sun flipping it many times after, a serious cleaning. .