I'm trying to run and internal fluid flow analysis and one of my parts has slots wrapped around a cylinder. They also wrap along the top which is like a half dome. I have attached pictures of the original part and my attempt at placing lids. I thought it would work, but during the check geometry I get a ton of zero thickness errors and face intersection errors. Wondering if someone could help me solve this? I made the lids by placing a plane off the slot, converting sketch entities, then doing a mid-plane offset extrusion.

Any help would be much appreciated.