There didn't seem to be on my car when I replaced said centre section. Metal to metal seemed to be the order of the day. The joint can/does twist slightly when on the move and uses spring bolts so is this why, or am I missing something?

 

The gasket should be there although it doesn't look like an ordinary exhaust gasket.

Check for a circular "brillo pad" around the outside edge of the downpipe.

Dark (Mark)

 

Scoobysnacks.

When I changed my OE downpipe to the scoobysport item, I had the same symptoms as you did (in your other post) before I realised that I hadn't retrieved the old gasket off of the downpipe!
The end of the downpipes have a flange with a short length of tube sticking forward.
The gasket is like half of a large olive (in case you are familiar with plumbing) with a flat back that sits against the flange and a chamfered front which wedges into the mid section (as you tighten your spring bolts).
I had to prise the old gasket carefully off of the old downpipe and because of all the old crap on it, it actually looked like one solid piece.
I suspect that your gasket is either missing from a previous installation (or has got stuck in the old centre section) or is in poor condition.

My car incidentally is an STi4 and the SS downpipe was previously fitted to a UK car.

Neil.

 

I checked the end of the downpipe again yesterday and as you thought might be the case Neil, there is a gasket on there but it was so dirty I thought it was part of the pipe. As Dark says I could also see close up that the surface had a brilo pad effect but was worn smooth - does this mean I require a new rougher surfaced one for a better seal?
Thanks for your comments.