the precision does matter when you are drawing it. Part of your problem is the precision setting you are using is much too coarse for the size of the objects you’re drawing. This makes it hard for you to get good results. It’s as if you’re trying to make baby spoons with a chainsaw.
There was so much bad geometry in your model it was easier to abandon it and redraw the part from scratch. By starting with clean edges, it was a simple matter of making a solid component. I also limited the number of sides on the circles to 48. You had them at 180 sides which for the small size of the holes is ridiculous overkill. It created a bunch of liabilities with no real benefits.
After I had the shape drawn, I made it a component and confirmed it to be solid. (It was from the beginning.)
Next, I opened it for editing and drew a cutting plane through the center of it…
…and used Intersect Faces to cut the faces at the cutting plane.
The next steps make it possible to have the left and right halves but you have to follow along exactly.
Create two layers, one called “Left” and the other called, “Right”
Select the component and hit Edit>Copy to copy it to the clipboard.
Select the component and assign it to the Left layer.
Turn off the visibility for the Left layer.
Hit Edit>Paste in place.
While the pasted copy of the component is selected, assign it to the Right layer.
Right click on it and choose Make Unique.
Set the camera to Parallel Projection and Top View.
Open the component for editing.
With right to left selections, select the left half of the component.
Hit Delete.
Erase the edges of cutting plane.
Correct the face orientation along the cut line if needed.
close that component and turn off the visibility of the Right layer.
Turn on the visibility of the Left layer
Repeat the steps of editing the component but this time remove the right side instead.
That same process will work if you want to split it horizontal and for any other shape.
In the case of the left/right split, if one was thinking ahead a couple of steps, you could leave out the counterbore on the near leg. Split the component in half and then copy and flip to make the counterpart. Make unique and then add the counterbore in the approriate location.
If you make a good clean selection of the half after the Intersect routing has completed, you could move a copy off to one side and then erase the original half.