LS8 Intake leaks

[Gus_Mahn]

Anybody experience intake vacuum leaks on a LS8? My car has a strange surging cold idle when it's below 25F outside. It's better now that it's warmer outside. It's also occasionally set lean codes. I smoked the intake while the car was cold, and found a small leak between the upper and lower intake on cylinder #1. Only the lower gasket is serviced. From Ford you have to buy the whole intake to get the square keyed o-ring that goes between the upper and lower intake. I believe the o-ring goes into a groove on the plastic upper and sits on a flat aluminum flange on the lower. I've been thinking about pulling it apart and using Ultra Black Silicone to try to seal it up. Any thoughts on this?

 

[joegr]

I don't think that you can get it apart (the metal and plastic parts of the manifold) without breaking the plastic, but I haven't tried it.
There was at least one member that posted about having a leak or leaks between the plastic and metal parts. He or a previous owner had tried glue or sealant that didn't work.