Manifold/header/muffler/tail Pipe problems of the 2002 Mazda MAZDA6

On cold starts there is a loud ticking sound from the front of the engine. Once engine warms up the ticking goes away. We brought our 2002 Mazda mpv to a local certified mechanic and he diagnosed a cracked front exhaust manifold. We called customer service at Mazda to report this problem and per Mazda since we exceeded our warranty by 5 months it will not be covered. After asking us about our repair and maintenance history with Mazda we reported having automatic transmission service done, brake service, and coolant flush service done at the dealership. The gentleman at Mazda asked us to hold so he could talk to the supervisor. When he returned he asked about the oil changes. I stated that I do those every 3,000 miles. After putting me on hold again, he stated that he could not help us after all. When we bought the van I asked if I could do my own maintenance and would it void any warranty problems and the salesman said "no". I went to another mechanic who specializes in exhaust and emission systems. I explained the situation to him and he said he would look into for us. He called back 3 days later and stated that there seems to be several complaints about the same situation we are having. In doing a national parts search at all national salvage yards to find an exhaust manifold for the van he found one in florida, but it also had a crack in it and was told that they have had numerous inquiries about the same exhaust manifold part. We took it upon ourselves to do research on the internet about this problem and was surprised to find numerous complaints of cracked exhaust manifolds on Mazda mpv's. We were quoted over $1,000 to fix this problem, but we feel after consulting with several mechanics this problem should never occurred and the exhaust manifold on these engines are most likely defective from the manufacturer. What is our next step? better business bureau??.