What can I use to clean the Krell faceplate?

A Shotgun. =)

I would start with something mild like mineral spirits.

Thanks Albert!

Simichrome from competitive chemicals, a German polish that if used with a soft cloth will not harm the surface.

Go VERY EASY with the polishing, only in the direction of the graining on the face place and stop, allow to dry and then polish off gently. If a time or two of that does not remove it, you probably wont get it off.

I did use chemicals on the face place of one of my preamps some years ago with great success, but it was risky. I used Acetone and MEK, but some of these attack plating and lettering and I would advise only if you are well experienced with these.