OK, some background. Picked up a 2002 WRX Wagon a couple of weeks ago. It looked nice and clean, unmodified, and just a few miles shy of 100,000. The struts were blown beyond recognition and it had what sounded like a minor exhaust leak in the front, but otherwise it seemed mechanically sound so we went ahead and bought it.
Fast forward a weekend or two and I finally have it on stands and can give it a proper inspection. The car spent the first 8 years of it's life in NY so it's nice and rusty underneath. The heat shields have almost completely biodegraded, but underneath the shields, the manifolds and crosspipe actually look pretty clean. I verified that exhaust was pooting out between the joints, so I ordered some replacement gaskets and figured that would fix it.
Now that I've gotten it all apart and replaced the gaskets, it is still leaking! I replaced both manifold-to-head gaskets, both manifold-to-crosspipe gaskets, and the manifold-to-uppipe gasket. I torqued the bolts/nuts per the factory service manual (don't remember exactly, but IIRC it was somewhere around 20 ft/lb), and I still have leaks at the right manifold/crosspipe and right manifold/uppipe joints. I tightened them more, but still leaking right out the side between the flanges.
I used thick grimmspeed gaskets, so I don't think the gaskets are to blame, and I doubt that the flanges could be bent as they're pretty stout. Is there a better way, or some sort of gasket sealant I can use in addition? I wouldn't worry about it if it was just noisy, but the idle is kind of wonky and the car feels like it is "fluttering" while accelerating at moderate throttle and I think the pre-turbo exhaust leaks could be causing that.
Any tips on how to get those joints sealed up? Also, are the heat shields on this car necessary to protect adjacent parts, or can they be safely left off? Mine had to be mostly destroyed to remove so I'd be looking at buying replacements or doing some kind of header wrap if it were absolutely necessary I suppose.