Sketchup =>Slic3r Frustrations

I've been trying to print a file from a brain gear from Thingiverse, but the gear needs to be rotated to sit on one end. I'm doing that in Sketchup. I've installed the .stl import and export extension, and I can get the gear into Sketchup and rotate it. The gear has holes around its middle in addition to the big hole thru. One curious thing: the gear comes into Sketchup below the Z=0 plane, though if I directly import it into Slic3r, it's above the Z=0 plane. A picture of the gear is attached.

When I try to export from Sketchup and use the .stl export feature, I get a gear that isn't correct when I import into Slic3r and look at the view/cut window. The holes around the middle are filled in. However, if I export an .obj file from Sketchup and import the file into Slic3r and look at it in the view/cut window, it looks perfect. When I export in .obj, I have to select the "export two sided faces" option to get the holes to appear correctly.

Then, if I slice the gear from the .obj file, I get an extremely tiny file (tens of kBytes) that only prints one layer. I don't get the whole gear.

The .stl files with the filled in holes appear to slice and create printable files.

How do I get the whole gear with the holes just like in the view/cut window?

I've not used the other applications, but I would do it using OpenScad - here's how (it's quick & easy)

1) Download and install OpenScad from [www.openscad.org]
2) Download the short Scad file attached to the same folder you have the STL file.
3) Double-click on the Scad file and it should open OpenSCAD to a project with the following 2 lines.

rotate([0,90,0])
import("gear.stl");

4) Change the name of the STL file inside the quotes on the 2nd line to whatever your file is named (keep the quotes, brackets and semicolon).
5) Press F6 to cause OpenSCAD to render the file (it may take a while). You may have to zoom in or out to see anything (click in yellow window and use the mouse wheel).
6) If there were no errors (don't worry if it is above or below or to one side of the axis), click on the "design" tab and then "Export as STL"

Dave