Is that where your oil leak is coming from (would be better than the rear main seal)?
I replaced the covers because the gasket for the spark plug tube is molded into the cover and isn't designed to be replaced separately. I saw a video of someone using a small rotary tool to try and cut the gasket ring out of the cover to replace it but it was really more work than it's worth.
I went with some cheap Amazon covers (Boxi left and right engine valve cover gasket replacement for Nissan...), but you can get OEM from Z1Offroad if you prefer (OEM Frontier / Pathfinder / Xterra 4.0L V6 Valve Cover & Gasket Kit) or other source- I have no relation with Z1, just noticed they have them when researching my own.
Some RTV for the front corners of the valve covers.
Spark plugs if it's anywhere close to time to change them.
Get the intake manifold gaskets:

I also recommend the breather hose 3pc kit:

Cheap hose pliers from Harbor Freight helped:

Wasn't too bad but was a little time consuming.

New on top, old on the bottom (you can see how flat the gasket is on the old one compared to the new):

 

leak is showing along rear third of covers on both sides...thanks for all the info...my wife says I no longer have any excuses...now I just need to get in the mood to tackle this...went ahead and ordered OEM as pricing wasn't much higher (quite shocking actually)

 

Wow such a rip off to have to buy the valve covers as well in order to get the spark plug gasket!! Unbelievable!! Such a rip off!! Such is life I suppose 😞

 

I'd measure them there's probably the same ones used on other models & brands found out this back in 2001 with spark plug tube seals for chrysler cross reference

 

Yes, I've seen a video where a guy found some the same size. The problem is that they are molded INTO the valve cover.