How to Seal Chambers
Here's what worked well for me.......get some moose tape from (DennisKirk). Comes in packages of two 10" x 3/4" strips. Using scissors, cut them in half lengthwise giving you four strips (one extra in case you screw up). Prepare the collars by using a dremel cone bit to lightly chamfer the groove so the tape will not catch on the edges - if it does, it will smear and not give you a good seal. Thoroughly clean both the collars and the headers with denatured alcohol - take your time to make sure you get everything completely cleaned out. I used a bunch of square toothpicks broken in half to carefully scrape the goo out of the collar trench and get the walls nice and clean.
Now you are ready to mount the collars, be very liberal with copper permatex on both sides of the copper gasket and the collar flange and mount them. A lot of RTV will squeeze out and you can use your finger to wipe the excess off on the inside of the joint so it is smooth and completely filled in. I also use black steel socket head allen bolts - much easier than trying to wrestle with nuts/studs.
Now to mount the headers. Cut one end of a tape strip off squarely using a razor blade, carefully peel the backing and gently wrap it around the end of the pipe leaving about a 1/16" overhang. Go ahead and wrap over where you started and trim off exactly so there is a tight joint with NO overlap. Be careful not to wrap too tightly it will creep away from the butt joint if wrapped too tightly. Round the tape over the end of the pipe with your finger so the edge is curved and smooth.
With your finger, press a liberal amount of RTV into the mounting collar gap, take your time and make sure you get a lot pressed in there. Clean off the inside and outside well. Get in a comfortable position and slowly press the pipe onto the collar. Make sure you get it centered well and go slow. If the tape appears to be binding, back off and fix it. If all goes well, the tape will slide into the collar without binding and will completely disappear up into the collar. Once the pipe is on, mount the back and then using your finger smear RTV around the collar/pipe joint, smooth and clean it. Mount the spring and let it sit overnight.