Power steering pump advise.

[1BAGTO]

Recently installed power steering on my 1970 GTO. It is the billet pump (Saginaw pump) from March Pulley's. I can't seem to get the thing to stop leaking. It seems to hold pressure fine when I take it for a test drive, check when Im done, no leak. Wake up in the morning and there is a half dollar size puddle of power steering fluid on the floor. I have taken it off twice, and still no fix. I have tried teflon tape but to no avail. The leak appears to be coming from the upper left hole if you were looking at it from the back.

Any help would be great, Thanks.