Loose header

[Donhoejr jr]

My header going into the motor keeps coming loose. Is this a common problem? I've replaced the gasket three times now . I torqued the bolts down to what the manufacturer says on the last two I replaced. It's good for a ride or two then it comes loose again. I even tried torquing it down when it's hot and it didn't help. It a dg head pipe if it matters. The muffler is bolted down in all three holes and the joints have sleeves on them to keep them from leaking.