I replaced the whole thing with a replacement from HDI about three months ago. Couldn't be happier. Just replace all of it, manifold, elbow and coupler along with the exhaust hose to muffler. Its to much of a pain to get it apart to not do so. The HDI bill was around $300 for all of it.
ditto what mike said! I replaced the whole thing with the HDI setup - worth the money, beautifully made all stainless. It's really hard to get the manifold and connector apart - and resealed - the threads are probably rusted and galled.
Well, I had already ordered just the elbow. I figured "I'm off work this week, so I'll just wail on that thing until it comes apart". After all, I have a big vice, a propane torch, penetrating oil, a hammer, and lever arms of varying lengths... Long story short: it didn't work! I clamped the elbow in the big vice and (after the penetrating oil, which has been on there for days) heated the manifold collar with a torch. Then I used a long ratchet extension in the hole of the manifold for leverage. No dice. Went out to the pickup and got the big breaker bar I use for changing the truck tires. No dice. Got a 5' length of heavy black pipe. Nope. In the middle there, I ended up having to attach my (heavy) workbench to the studs on the wall so it wouldn't rotate. It's not like I broke the exhaust manifold or anything, but it didn't budge one little bit. I did bend the pipe, though, and my vice may need some attention...
So after almost destroying my workshop, I just called HDI and changed the order to the full Monti: elbow, coupler, manifold, cooling water nipple, and gasket, all for only $335. I guess I should take advice more readily...