did u put the little reducer insert in the pipe where it bolts to the flange? There is a reducer piece that goes in the pipe to make it smaller and fit tighter so there is no leak.
Yup... try using the reducer and that may help. I had a nasty leak on my VRS O/R X because I forgot to install the little 2" piece of pipe but after I did the leak was gone.
If you can't find a specific item for sale anywhere you may could fab something off of a header reducer, I just cut the flange off of my stock H pipe but I'm guessing you probably don't have that. May check salvage yards too for a stock H to cut flange from.