Help with non-manifold geometry and stl file Pretty new to Blender and modeling in general and I've spent a couple days trying to figure out this problem. Can someone more knowledgeable take a look and give me some direction?
Background
Been working on modifying a 3d model in preparation to print, but have been running into what's become an insurmountable problem for me.
I've divided the model up into sections and added keys to help printing and assembly later. Have then exported each section as individual stl files to test importing and slicing in the print utility. All of the parts are fine except for one.
Issue
The problem section seems to have some geometry issues that I haven't been able to fix. There appear to be some non-manifold sections but I haven't been able to find a way to fix them. Have spent hours tinkering with the model manually to no avail. I've ran the section through Mesh -&gt; Cleanup, as well as trying to apply a combo of remesh and decimate modifiers. (The last 2 kept crashing Blender so couldn't make progress that way.)
The key hole on the bottom may be causing problems. The stl file that gets generated sometimes has errors in the slicer or completely disappears when I change the rotation of the section model.
Here's an image of the non-manifold sections selected.

Here's a link to the blend file of the model https://drive.google.com/file/d/1ESKfCxDuTgUELPmL98NK5f8HZFfpfKw9/view?usp=sharing.
In the blend file, each model section is labeled like &quot;sword-0&quot;, &quot;sword-1&quot;, etc. The problem section is &quot;sword-0&quot; and should be the only one visible on opening the file.
There were three main issues with you non-manifold mesh:

Faces going through other faces - You need to reconnect them vertex to vertex.
Disconnected edges (with gaps) - hard to notice, check for non-manifold vertices
Holes in mesh - just fill them through Vertex &gt; New Face (F)

To check for non-manifold geometry try this:

Select &gt; All by trait &gt; Non-Manifold. This will highlight all non-manifold vertices. There should be none.
Check face orientation - this will also reveal small holes and missing faces


Faces going through other faces

Disconnected edges (with gaps)