Leaking PS gear box at top-need help

I feel silly such a thing as a leak is stumping me but I need some help...

Attached is a pick of the leaky area.
It's the little cast aluminum piece on the low pressure side that bolts to the steering gear itself.
I've always had a slow leak, and wanted to get this done.
After removing this piece i realized there was no gasket and just a little o ring in a recess.
So I tried cleaning the 2 surfaces and making a home made gasket. Nope leaked like crazy.
Tried installing a new o-ring, .09 thick but was too big on the OD, so I split and put the "new" o-ring in and the ends matched pretty good. No I didn't glue the ends or anything, probably a big mistake because, leaked like crazy.
Tried putting the same old o-ring in from another old gear box i had, and leaked like crazy.

So, should I be "sealing" these surfaces with some kind of gasket sealer/maker?
What and where to get the correct new o-ring? I'm not sure what to call this component.
Valve on power steering pump gear box? I just don't know.
Thanks in advance for any help, and my garage floor thanks you for any help in keeping fluid off it.