I'm kind of in the same boat as you. I went mudding (claying?) and the clay that shot up covered my exhaust the other day and i had not a single tick. as time consuming as this was i would spray off the clay in sections too pinpoint where exactly the leak was coming from. found that i had a crack in my manifold. i'm sure you could find an easier way than this but i just thought id share it with you since it worked very well for me. not saying go mudding and see what happens but get some sort of clay and cover sections of your exhaust where you think it might be and that will help you pinpoint it.