Lemme guess: it's the passenger side that's split? That's the split one on mine...and poorly welded back up to boot.
Now that it's quiet in the back, it's definitely quieter and cooler back there while riding. Even when the AC isn't running (better breeze back there).
On the TQ: go to your local parts place and get a rebuild kit for a ThermoQuad (it's a general kit, I think) and follow the instructions carefully. The bf just bought a replacement 6518s on eBay since ours has seized adjustment screws so I just ordered another rebuild kit. I'll have it tomorrow, so I'll put the part number up then. When we rebuilt the one on our rig, everything that could be adjusted was about as far out of spec as possible (and one thing wasn't put back together properly).
Oh, and here's a link to a bunch of manifolds on eBay:
http://motors.shop.ebay.com/__?_from=R40&_trksid=p3841.m39.l1313&_nkw=440+manifold&_sacat=
