What is this dishwasher drain solenoid seal part & how can I replace it?
This part is a shaft seal (the links below), you might want to get the push-on nut also (GE part number AP2059046), as you may have to cut it off to install the seal.



searspartsdirect.com, Part number: WD08X0181, Substitution: WD8X181. (Part may differ in appearance but is a functional equivalent)

appliancepartspros.com also shows this seal as: Part Number WD8X181