looks like a punch mark for id'ing the caps...that diff been apart before? (my dana had a "Y" stamped on them and the housing from factory, one side sideways...)

 

It's not the punch mark. The punch mark is right over it. It's like a knick right under it.

So is a little RTV on the inside okay?

 

Ya It's fine to have 'some' rtv smoosh inside.

What I usually do is run a continuous 1/4 inch bead around the cover and circle the bolt holes.
let it sit for 10 mins then bolt it on. I refill immediately with fluid.
No problems 99.9% of the time.

Don't stress, this ain't exactly rocket science...

 

Yeah I know it's not rocket science I just am super cautious as I don't want to cause a problem with something. I'm just a perfectionist when it comes to doing work on my vehicles. The Right Stuff says to put it backtogether within 5 minutes so I put it on shortly after I put the rtv on there. Then on the rear I filled it up right away on the front I let it sit for a few hours while I did other stuff.

 

If any of the rtv got inside it would just get pulverized by the gears or fly around harmlessly. I've done the diffs twice and never worried about the seal. It's fine.

 

You and I are the same hometheaterman, I like to ponder questions about things that most people think are non issues or would never think of. That's how engineers think though.