exhaust leak

[tipota]

i had an exhaust leak in my down pipe, and i tried to change it but someone welded the downpipe to the headers. im really broke right now so i bought some headers off eaby that also came with a downpipe. it was a pain and the ass to install, but i finalyl did and the problem was fine for about a day. now i have another exhaust leak. is it most likly a gasket leak? how do i find where it is, and are there any special steps to installing gaskets that i might have missed?