Dishwasher top shelf would be fine for plastics without paint. Make sure not to use the heated drying which some machines get amazingly hot. Most plastics are fine in the dishwasher such as Acrylics, ABS, PC, PS, nylons, etc. that have pretty high melt temps. PP and PE(Low density) are even fine on top shelf dishwasher but can deform in the lower rack dishwasher if near the heating element due to their lower melt temp , although I don't think these are used much in pinball machines.