[Dominik]

Bolt down one header tight as a starting point and let the three other loose and insert them all in the collector. Then tighten. It helps if you take the louvers out to reach inside. You might want to use studs for the headers. Helps positioning them and the serrated face nuts never come loose.

I had 3/8" individual flanges and a minimum of sealer (no gasket). Depending on the backpressure of your sidepipes you will not have any blow-by. Not even at the slip in collector. I advise using slip-ins with springs versus bolt ons.

I tried to teach people since many years that bolt on cause the pipe hangers to crack. Ducati listened ;-)