by the way i think other's have mentioned it before but best off to re-assemble from the front forwards to get a proper seal the flange fit is excellent when it's assembled properly (u shouldn't need any putty at all)
if u use a second hand y pipe best off to hit it with a wire wheel on a bench grinder to clean it up properly (and corresponding cups too)
here are a couple of earlier threads with some useful information about sourcing and installing GS exhaust components. Apparently Walker do list some GS exhaust components, according to Chris. And Gerry has found some superior clamps for the joints, if your old ones are shot (which they often are on a GS).
Yeah, I'm not sure what make of front pipe I ended up getting from Auto France (wasn't a Citroen one) earlier this year, but it sure was pricey
I'm told that Walker do the whole system, but I don't like my Walker muffler -- I had to hit it with a hammer to make it fit, and it goes "burble burble brrrk burble" at idle Could be my engine of course :joker:
I've had endless trouble getting the exhaust tight on my current car, stemming, I think, from a third-party Y-pipe that has the mouting bracket about 10mm too far back... there have been some naughty words said about the whole thing.