I guess different dishwashers will get hotter inside than others. Mine makes my counter quite warm. I wouldn't risk it. My concern as well would be melting, or even some deformation. Different plastics have different melting points. Printed Key Labels, may also be removed in the dishwasher. Having cleaned a few C64s, it is not that bad hand scrubbing the and the keys. Then no risk of causing the keys or case to deform. If you were to put the key caps in, they would be flying around inside there unless the plungers were still attached, but you wouldn't want the pads on the bottom of the plungers, they could come off and get lost, and if they didn't, they may no longer be properly conductive. The springs shouldn't really be left in there either, your mileage may vary though.