Jeff: I use Members Mark grill and oven cleaner. Best cleaner I have found for getting the gunk out of the firebox. I don't really know of any part of the Silver B that it would harm simply by using it to clean the cook box area.
What hardware is "siezed"? PB Blaster, WD40, Liquid Wrench are some of the more popular penatrating oils for freeing rusted and frozen nuts and bolts. But, some nuts and bolts on your grill might just not come unstuck no matter what. Applying heat will also aid in freeing rusted and seized hardware.