Sealing Dynomax headers

Ive cut my headers between ports with good success but dont overtighten or you will really bend the flanges as theres less support.Also my brother used to work at an exhaust shop and turned me onto an exhaust sealer that is awesome,its a tar/silicone like substance and works very well but doesnt harden like concrete so you can actually remove your header.Its actually available at napa and its there product,you just coat both sides of the gasket and go,I use it on every header and never have problems.