Eletric Motor Water Housing

thingiverse

This is an outer shell for an electric motor that I've acquired. The motor required a cooling system, prompting me to start designing a water cooling shell around it. The model appears flawless within the 3D modeling tool, but when opened in a slicer, the hole intended for the motor is unexpectedly filled with material. Despite my efforts, I'm still unsure about what I'm doing wrong, so I'm uploading this here in hopes that someone can offer assistance.