Mid-pipe-to-axleback muffler Gasket question???

[blacksandiegovitz]

Just installed a megan header and nitto mid-pipe hooked up to my hks hi-power exhaust and there is a desent exhaust leak where the end of the mid-pipe meets the muffler flange(re-used stock donut gasket) . I read a couple post saing not to use to stock gasket(donut) with this set-up cause its too small , so what gasket is everyone with a similar set-up running
thnx