For some reason the photos aren't showing up in this post anymore. I've copied the write-up over to here so you can still see the pictures.
Like most of us with the 3.8, I had a crack in my driver's side manifold. I read about a product called ThermoSteel on another forum, which is an epoxy-like adhesive that claims to be good for temperatures up to 2500F (JB-Weld is only good up to 600F, so is not suitable for a manifold repair). The manufacturer claims that this stuff is as strong as a hot weld. For $8 at AutoZone, I figured I'd give it a shot. We'll see how long it holds up over time. I'll report back here with an update from time to time to let you know how it's holding.
It's a pretty simple procedure, and took me all of 20 minutes to do. The hardest part was getting the rear bolt off of the heat shield:
There's not much room to work in there, so a U-joint and a long extension or two are needed. It's a 10mm bolt. These are very tight and probably rusted on, so you might want to spray some penetrating oil on first and let it sit for a few hours or overnight.
The other bolts are a little easier to reach. The lower one takes a little finesse too, because there's not much room. You'll probably need the universal joint there too.
Once you remove the bottom nut, the two pieces of the heat shield will come apart. It might be easier to pull the top section off if you remove the spark plug wires and get them out of the way. Once you have the heat shield off, you'll see this :
Grab your package of ThermoSteel:
Read the directions on the package. Pretty self-explanatory. You need to mix it very thoroughly, and make sure you get all the gunk that has settled to the bottom and mix it in. I used a flathead screwdriver to mix it up. It should be about the consistency of toothpaste when you're done.
Smear it on with a brush or your finger. Put it on thick. The instructions say up to 1/4 inch thick is okay. Mine was just a hairline crack - for a wider opening you might need to pack it down in there or use some wire mesh to cover the hole first.
Let it cure for five or six hours. The instructions say to heat the surface gradually after it cures...I'm not sure how you can really do that with an exhaust manifold, but I just started the engine and let it run for a minute or two, then shut it down. Then I waited a half hour and started it again. Repeated this three or four times and figured that was good enough. Then I reinstalled the heat shield and let it sit overnight before running the engine to full temperature.
That's all there is to it. I'll let you know how it holds up over time.
*** Update #1 8/04/2012 : 3 months and still holding ***
*** Update #2 9/11/2012 : 4 months and still holding ***
*** Update #3 7/08/2013 : 15 months and still holding ***