72 power steering leak/identify this hole!

[dukcaln]

so I have been meaning to get to the leaking power steering pump. I thought it was leaking from the fitting on the bottom that the hard line enters the rear of the pump, but after filling the pump and sec later a super leak appears. I crawled under and to my surprise I found this hole in the back of the pump above the fitting but below the fill next. so why is there a hole here and what if anything goes there? Is it a plug or something.... soory for the crappy photo but it was hard to get my cell phone up there to take a good picture...