Advice on how to separate muffler from the down pipes

I want to drop my muffler down and away so I can seal the back of the transmission with The Right Stuff sealant as oil is oozing out of the gasket and leaking where the bolts secure the back cover to the transmission.
Can anyone advise me on how to separate the stainless muffler from the down pipes. I am currently soaking the joints with WD 40. Photo attached!
Many thanks
Dennis 69 OTS

Maybe with this technique.

It might just be easier to drop the whole system by taking down pipes off at the exhaust manifold. Then with five more bolts the entire system comes out as one piece. I have found using double U joints and long extensions makes getting to all the exhaust manifold down pipe bolts possible. Good light and a helper up top would be a good idea.

First, get a real solvent such as PBBlaster or Kroil. Second, assuming the outer piece has slots at 12:00 and 6:00, use a thin chisel to drive in and spread the pieces, at least as far as the slots go. Yes, heat may help, although it gets heated every time you operate the car, which is probably why it gets fused together in the first place. Tighten that clamp shown in your photo at a convenient place and use it as a location to hammer upon. Place another heavy hammer on the muffler so the hammer force is directed into the joint. I would not argue with Bill’s approach. The exhaust manifold bolts are no picnic but if all you are trying to do is get it out of the way, his approach will work fine.

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I find it works better to just drop the whole thing, then I can clamp the pipe in a vice and walk the muffler off. Trying to walk it off on the car just flexes the headpipes, then you end up needing new headpipes when the flex joint cracks (I just welded modern flex fittings into mine when it broke). Yours doesn’t look corroded so I don’t think penetrating oil is going to make a big difference. It has been my experience that the muffler clamps distort the pipes locking them together, so after you get them apart use a pipe expander to get it round again.

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Many thanks for all your suggestions.
I will try a propane torch heat and if that does not work I will undo the exhaust manifold nuts and drop it down!
Dennis 69 OTS

I got the muffler separated from downpipe just by soaking with liquid wrench.
I then hit the muffler hard with a heavy hammer cushioned by a small block of wood

When I reassemble it, should I use a little high temperature neverseize??

Dennis 69 OTS

I would say no. That would allow the pipes to move. I would use a muffler “glue”(?) type product that is designed for that. They seal without severely crimping the pipe and if you get the right one, they are designed to let go when you apply the torch.