I'm wondering about the joints in the exhaust pipes.

I should be able to get the turbo mounting plate and the exhaust manifold to the turbo in place - but what is the best way to put these joints back together? Do I need to use paste/putty etc or can they simply be bolted straight back together? Is it worth replacing the bolts/nuts? There are four of these joints to do, on the short pipe sections.
Last thing I want is to have to take the whole bloody thing back apart when it starts pouring out smoke!
