What method do I use to clean the white felt on a base drum beater? It's soiled with grease spots and is a dirty, off-white color. It is the beater operated with the foot on a drum kit. It's about 1" squared.

Given that actual felt used to be wool, rather than it's modern counter part which is a high blend of polyester, or missing the wool completely, it was not technically washable as it would lose both it's shape and size. I recommend treating it like a suede product and using a dry cleaning spray and stiff brush or simply coating it heavily with white chalk, working that into any oily stains and brushing it back out thoroughly with a vegetable brush, re-treating any area as needed. A stiffer metal bristle brush will be needed on some stains to break up the compacted felting.