Well shoot, got the new seal and reinstalled the pump on the NAA. Same leak. It is situated up against the block so I can't see what it going on at the back side but it is still leaking back there. So apparently it was not the O-rings between the pump and the manifold flange.
I will check when I remove it next time to make sure the O-rings stayed put where they needed to be.
I suspect though that the leak is coming from the pump. I rebuilt the entire pump and may have just put it together wrong or a seal did not stay put.
Ugh! I may have to come up with some type of pressure test of the pump to force it to show the leak. : (
Will try now to come up with the rebuild procedure again on that piston pump. I will need that if I take it apart.

Having fun on this hydraulic pump leak. Took the head off the pump and I think the gaskets for the head, (2) one inner and one outer according to the parts diagram, may be the issue. I may have put the outer gasket on in the wrong orientation. : (. Whip me, spank me, send me home. I called Messick's again and ordered both gaskets. So in about a week and half, I should be able to put it back together again. Couldn't see any other reason that it could leak. Time for a nap.

o-rings stayed in place so that isn't the problem. I think it leaking out around one of the bolts on the front housing. It's either that or the top allen screw plug is leaking. tried to watch for the leak but just could not see it clearly

Don't ask how I know however, if you don't have ALL the gaskets oriented correctly, guess what, it leaks! Got to busy talking to my grandson one time and it happened. Moral of the story, I can buy lots of gaskets, treasure the time with my grandson.

Thanks for the response Cowboy. I believe you are most correct, it can happen and did with this pump gasket.

In respect to you valuing your time with your grandson, I like your thinking. Way cool.

Mike in CO