Hi Mark, so there are a few different little slivery surfaces in that area shown above, it's kind of a mess in that spot. But the area on the opposite side is completely clean. Since it looks like this piece is supposed to be symmetrical probably the easiest way to finish it would be to cut it in half with the Trim command and mirror the good half and then join those pieces together, all done after deleting the faces that you don't want for the inner portion.

.... But also looking at it a bit more the piece seems to be slightly rotated, like the top edge is not completely flat going along the x axis, it's like 1 degree rotated from horizontal. So that could potentially complicate making a good mirror of it.

- Michael

Hi Mark, I've attached here a finished version - I used the steps I described above to select and then delete the faces for the inner portion.

Then I drew in a dividing line from the midpoint of the top edge to the midpoint of the bottom arc, which is not an exact vertical line though because the shape is slightly rotated. Then using that line I used the Edit > Trim command to slice the object into 2 half pieces, deleted the half with the messy area, then mirrored the good half and then joined the mirrored pieces together to make a solid.

Hopefully this is the result you were trying to get.

- Michael