Hi Ranger I am collecting parts to do the upper and lower manifold gasket replacement also.
The plastic elbow is GM # 24503423 and seals with an o-ring on each end $7.89+tax @ dealer. You need to pull the belt tensioner assembly to do the job right. There is another o-ring on the back side of the tensioner that will have to be replaced. If you use the Felpro lower gasket set # MS 95809 it comes with spare o-rings.
Check out these pictures from “mkaake” showing the difference between stock gaskets and Felpro replacements. I have no idea why GM put those 4 little notches in each coolant opening. Look at the pictures and you can see that is where the lower manifold gaskets fail.
If they would only upgrade the gaskets so that the rubber wrapped around the black plastic so that coolant can not come in contact with the plastic and eat it. The coolant ports, in the lower gasket set, should look like the 6-intake runner seals in the new upper gasket GM # 389017554.
Here is another good link.
Sure was nice of GM to leave that sharp edge on the O2 sensor to cut up our knuckles.
Will not work on the backside of the motor until I slip a piece of slit rubber hose around the O2 sensor. Also take pieces of vacuum hose and put it on any studs protruding from the firewall.
The local Wally-World now sells Kimberly-Clark “SAFESKIN” purple nitrile gloves. These come 40 to the box and cost about .10c each but sure do save the hands. Now if I can only remember to put them on before picking up a ratchet.