Exhaust leak at Gasket

i must be doing something wrong, i have had a leak at the lower part of the gasket between the cat and the rear exhaust section 3 times now. just started leaking again. each time, i get new bolts and a new gasket from the dealer. it's ok for a while, then slowly over time the exhaust gets louder and louder. i checked over the weekend and i cannot tighten the bolts any further. the leak is right at the 6 oclock position between the cat and the rear exhaust piece. should i be doing anything else when i replace this piece?

 

I think there are exhaust joint sealants for these joints http://www.amazon.com/s?ie=UTF8&page=1&rh=i:aps,k:Exhaust Pipe Sealant

 

awesome, thanks guys