how to change my exhaust to manifold gasket ?

ive got a leaking gasket at the exhaust manifold my downpipe to manifold is held together by two bolts that wont tighten up anymore but will easily come free should there be springs inbetween the bolts and downpipe to give pressure as mine hasnt got any i had the gasket done about 3month ago by a garage and my car came back with the gasket done but now leaks again can anyone help